### Infimum and Supremum of the Set of Real Numbers. Measure Theory

by
Jozef Bialas

Copyright (c) 1990 Association of Mizar Users

MML identifier: SUPINF_1
[ MML identifier index ]

```environ

vocabulary BOOLE, ARYTM_3, SEQ_2, ARYTM, LATTICES, ORDINAL2, TARSKI, SUPINF_1;
notation TARSKI, XBOOLE_0, ZFMISC_1, SUBSET_1, ORDINAL1, NUMBERS, XREAL_0,
REAL_1;
constructors REAL_1, XREAL_0, MEMBERED, XBOOLE_0;
clusters XREAL_0, SUBSET_1, XBOOLE_0, MEMBERED, ZFMISC_1;
requirements SUBSET, BOOLE;
definitions TARSKI, XBOOLE_0;
theorems AXIOMS, TARSKI, ZFMISC_1, REAL_1, XREAL_0, XBOOLE_0, XBOOLE_1;
schemes XBOOLE_0;

begin

::
:: -infty , +infty and ExtREAL enlarged set of real numbers
::

definition
func +infty -> set equals
:Def1: REAL;
correctness;
end;

canceled;

theorem Th2:
not +infty in REAL by Def1;

definition let IT be set;
attr IT is +Inf-like means
:Def2:IT = +infty;
end;

definition
cluster +Inf-like set;
existence proof take +infty; thus thesis by Def2; end;
end;

definition
mode +Inf is +Inf-like set;
end;

canceled;

theorem
+infty is +Inf by Def2;

definition
func -infty -> set equals
:Def3: {REAL};
correctness;
end;

canceled;

theorem Th6:
not -infty in REAL by Def3,TARSKI:def 1;

definition let IT be set;
attr IT is -Inf-like means
:Def4:IT = -infty;
end;

definition
cluster -Inf-like set;
existence proof take -infty; thus thesis by Def4; end;
end;

definition
mode -Inf is -Inf-like set;
end;

canceled;

theorem
-infty is -Inf by Def4;

definition let IT be set;
attr IT is ext-real means
:Def5: IT in REAL \/ {-infty,+infty};
end;

definition
cluster ext-real set;
existence
proof
set x = -infty;
A1:   x in {-infty,+infty} by TARSKI:def 2;
take x;
thus x in REAL \/ {-infty,+infty} by A1,XBOOLE_0:def 2;
end;
end;

definition
func ExtREAL -> set equals
:Def6: REAL \/ {-infty,+infty};
correctness;
end;

definition
cluster -> ext-real Element of ExtREAL;
coherence by Def5,Def6;
end;

definition
mode R_eal is Element of ExtREAL;
end;

definition
cluster -> ext-real Real;
coherence
proof
let r be Real;
r in REAL \/ {-infty,+infty} by XBOOLE_0:def 2;
hence thesis by Def5;
end;
end;

canceled;

theorem
for x being Real holds x is R_eal by Def5,Def6;

theorem Th11:
for x being set holds
x = -infty or x = +infty implies x is R_eal
proof
let x be set;
assume x = -infty or x = +infty;
then x in {-infty,+infty} by TARSKI:def 2;
hence thesis by Def6,XBOOLE_0:def 2;
end;

definition
redefine func +infty -> R_eal;
coherence by Th11;
redefine func -infty -> R_eal;
coherence by Th11;
end;

canceled 2;

theorem Th14:
-infty <> +infty
proof
assume A1: -infty = +infty;
consider x being Element of REAL;
A2: x = REAL by A1,Def1,Def3,TARSKI:def 1;
for X,Y be set holds not ( X in Y & Y in X);
hence thesis by A2;
end;

::
::       Relations " <=' "," < " in the set of r_eal numbers
::

Lm1:
for x being R_eal holds
x in REAL or x = +infty or x = -infty
proof let x be R_eal;
x in REAL or x in {-infty,+infty} by Def6,XBOOLE_0:def 2;
hence x in REAL or x = +infty or x = -infty by TARSKI:def 2;
end;

definition
let x,y be R_eal;
pred x <=' y means
:Def7: ex p,q being Real st p = x & q = y & p <= q if x in REAL & y in REAL
otherwise x = -infty or y = +infty;
consistency;
reflexivity by Lm1;
connectedness
proof let x,y be R_eal;
assume
A1:     not(x in REAL & y in REAL implies
ex p,q being Real st p = x & q = y & p <= q) or
not (not(x in REAL & y in REAL) implies x = -infty or y = +infty);
per cases by A1;
suppose that
A2:  x in REAL & y in REAL and
A3:  not ex p,q being Real st p = x & q = y & p <= q;
thus y in REAL & x in REAL implies
ex p,q being Real st p = y & q = x & p <= q
proof assume y in REAL & x in REAL;
then reconsider a = x, b = y as Real;
take b,a;
thus thesis by A3;
end;
thus thesis by A2;
suppose not(x in REAL & y in REAL) & not(x = -infty or y = +infty);
hence thesis by Lm1;
end;
antonym y <' x;
end;

canceled;

theorem
for x,y being R_eal holds
((x is Real & y is Real) implies
(x <=' y iff ex p,q being Real st (p = x & q = y & p <= q)))
by Def7;

theorem Th17:
for x being R_eal holds (x in REAL implies not (x <=' -infty))
by Def7,Th6,Th14;

theorem Th18:
for x being R_eal holds x in REAL implies not +infty <=' x
by Def7,Th2,Th14;

theorem
not +infty <=' -infty by Def7,Th2,Th14;

theorem
for x being R_eal holds x <=' +infty by Def7,Th2;

theorem
for x being R_eal holds -infty <=' x by Def7,Th6;

theorem Th22:
for x,y being R_eal holds x <=' y & y <=' x implies x = y
proof
let x,y be R_eal;
assume that
A1:x <=' y and
A2:y <=' x;
x in (REAL \/ {-infty,+infty}) & y in (REAL \/ {-infty,+infty}) by Def5;
then (x in REAL or x in {-infty,+infty}) & (y in REAL or y in {-infty,
+infty
}) by XBOOLE_0:def 2;
then A3:(x in REAL & y in REAL) or (x in REAL & y = -infty) or (x in
REAL & y = +infty
) or
(x = -infty & y in REAL) or (x = -infty & y = -infty) or (x = -infty & y =
+infty) or
(x = +infty & y in REAL) or (x = +infty & y = -infty) or (x = +infty & y =
+infty) by TARSKI:def 2;
(x in REAL & y in REAL) implies x = y
proof
assume
A4:x in REAL & y in REAL;
then A5: ex p0,q0 being Real st x = p0 & y = q0 & p0 <= q0 by A1,Def7;
ex p1,q1 being Real st y = p1 & x = q1 & p1 <= q1 by A2,A4,Def7;
hence thesis by A5,AXIOMS:21;
end;
hence thesis by A1,A2,A3,Def7,Th14;
end;

theorem
for x being R_eal holds
x <=' -infty implies x = -infty
proof
let x be R_eal;
assume
A1:x <=' -infty;
-infty <=' x by Def7,Th6;
hence thesis by A1,Th22;
end;

theorem Th24:
for x being R_eal holds
+infty <=' x implies x = +infty
proof
let x be R_eal;
assume
A1:+infty <=' x;
x <=' +infty by Def7,Th2;
hence thesis by A1,Th22;
end;

scheme SepR_eal { P[R_eal]}:
ex X being Subset of REAL \/ {-infty,+infty} st
for x being R_eal holds x in X iff P[x]
proof defpred Q[set] means ex x being R_eal st x=\$1 & P[x];
consider X being set such that
A1:for r being set holds r in X iff r in REAL \/ {-infty,+infty} & Q[r]
from Separation;
X c= REAL \/ {-infty,+infty}
proof
let r be set;
assume r in X;
hence thesis by A1;
end;
then reconsider X as Subset of REAL \/ {-infty,+infty};
take X;
let x be R_eal;
hereby assume x in X;
then ex y being R_eal st y = x & P[y] by A1;
hence P[x];
end;
assume A2: P[x];
x in REAL \/ {-infty,+infty} by Def5;
hence thesis by A1,A2;
end;

canceled;

theorem
ExtREAL is non empty set by Def6;

theorem
for x being set holds
x is R_eal iff x in ExtREAL by Def6;

canceled;

theorem Th29:
for x,y,z being R_eal holds ((x <=' y & y <=' z) implies x <=' z)
proof
let x,y,z be R_eal;
assume that
A1:x <=' y and
A2:y <=' z;
A3:x in (REAL \/ {-infty,+infty}) & y in (REAL \/ {-infty,+infty}) & z in
(REAL \/ {
-infty,+infty}) by Def5;
A4:(x in REAL & y in REAL & z in REAL) implies x <=' z
proof
assume
A5: x in REAL & y in REAL & z in REAL;
then consider p0,q0 being Real such that
A6: x = p0 & y = q0 & p0 <= q0 by A1,Def7;
consider p1,q1 being Real such that
A7: y = p1 & z = q1 & p1 <= q1 by A2,A5,Def7;
p0 <= q1 by A6,A7,AXIOMS:22;
hence thesis by A6,A7,Def7;
end;
A8:(x in {-infty,+infty} & y in REAL & z in REAL) implies x <=' z
proof
assume x in {-infty,+infty} & y in REAL & z in REAL;
then ((x = +infty) & y in REAL & z in REAL) or
((x = -infty) & y in REAL & z in REAL) by TARSKI:def 2;
hence thesis by A1,A2,Def7,Th6,Th24;
end;
A9:(x in REAL & y in {-infty,+infty} & z in REAL) implies x <=' z
proof
assume x in REAL & y in {-infty,+infty} & z in REAL;
then A10: x in REAL & (y = -infty) & z in REAL or x in REAL & (y = +infty
) & z in REAL
by TARSKI:def 2;
x in REAL & (y = +infty) & z in REAL implies x <=' z by A2,Th2,Th24;
hence thesis by A1,A10,Def7,Th6;
end;
A11:(x in {-infty,+infty} & y in {-infty,+infty} & z in REAL) implies x <=' z
proof
assume x in {-infty,+infty} & y in {-infty,+infty} & z in REAL;
then (x = -infty) & (y = -infty) & z in REAL or
(x = -infty) & (y = +infty) & z in REAL or
(x = +infty) & (y = -infty) & z in REAL or
(x = +infty) & (y = +infty) & z in REAL by TARSKI:def 2;
hence thesis by A1,A2,Def7,Th2;
end;
A12:(x in REAL & y in REAL & z in {-infty,+infty}) implies x <=' z
proof
assume x in REAL & y in REAL & z in {-infty,+infty};
then x in REAL & y in REAL & z = -infty or x in REAL & y in
REAL & z = +infty
by TARSKI:def 2;
hence thesis by A2,Def7,Th2,Th6,Th14;
end;
A13:(x in {-infty,+infty} & y in REAL & z in {-infty,+infty}) implies x <=' z
proof
assume x in {-infty,+infty} & y in REAL & z in {-infty,+infty};
then (x = -infty) & y in REAL & (z = -infty) or
(x = -infty) & y in REAL & (z = +infty) or
(x = +infty) & y in REAL & (z = -infty) or
(x = +infty) & y in REAL & (z = +infty) by TARSKI:def 2;
hence thesis by A2,Def7,Th6;
end;
A14:(x in REAL & y in {-infty,+infty} & z in {-infty,+infty}) implies x <=' z
proof
assume
x in REAL & y in {-infty,+infty} & z in {-infty,+infty};
then x in REAL & (y = -infty) & (z = -infty) or
x in REAL & (y = -infty) & (z = +infty) or
x in REAL & (y = +infty) & (z = -infty) or
x in REAL & (y = +infty) & (z = +infty) by TARSKI:def 2;
hence thesis by A1,A2,Def7,Th2;
end;
(x in {-infty,+infty} & y in {-infty,+infty} & z in {-infty,+infty
}) implies x <=' z
proof
assume x in {-infty,+infty} & y in {-infty,+infty} & z in
{-infty,+infty};
then (x = +infty) & (y = -infty) & (z = -infty) or
(x = +infty) & (y = -infty) & (z = +infty) or
(x = +infty) & (y = +infty) & (z = -infty) or
(x = +infty) & (y = +infty) & (z = +infty) or
(x = -infty) & (y = -infty) & (z = -infty) or
(x = -infty) & (y = -infty) & (z = +infty) or
(x = -infty) & (y = +infty) & (z = -infty) or
(x = -infty) & (y = +infty) & (z = +infty) by TARSKI:def 2;
hence thesis by A1,A2;
end;
hence thesis by A3,A4,A8,A9,A11,A12,A13,A14,XBOOLE_0:def 2;
end;

definition
cluster ExtREAL -> non empty;
coherence by Def6;
end;

canceled;

theorem
for x being R_eal holds
x in REAL implies -infty <' x & x <' +infty
proof
let x be R_eal;
assume
A1:x in REAL;
-infty <=' x by Def7,Th6;
hence -infty <' x by A1,Th6,Th22;
x <=' +infty by Def7,Th2;
hence thesis by A1,Th2,Th22;
end;

::
::       Majorant and minorant element of X being SUBDOMAIN of ExtREAL
::

definition
let X be non empty Subset of ExtREAL;
canceled;

mode majorant of X -> R_eal means
:Def9:for x be R_eal holds x in X implies x <=' it;
existence
proof
take +infty;
thus thesis by Def7,Th2;
end;
end;

canceled;

theorem Th33:
for X being non empty Subset of ExtREAL holds
+infty is majorant of X
proof
let X be non empty Subset of ExtREAL;
for x being R_eal holds x in X implies x <=' +infty by Def7,Th2;
hence thesis by Def9;
end;

theorem Th34:
for X,Y being non empty Subset of ExtREAL holds
X c= Y implies
(for UB being R_eal holds UB is majorant of Y implies UB is majorant of X)
proof
let X,Y be non empty Subset of ExtREAL;
assume
A1:X c= Y;
let UB be R_eal;
assume UB is majorant of Y;
then for x be R_eal st x in X holds x <=' UB by A1,Def9;
hence thesis by Def9;
end;

definition
let X be non empty Subset of ExtREAL;
mode minorant of X -> R_eal means
:Def10:for x be R_eal holds x in X implies it <=' x;
existence
proof
take -infty;
thus thesis by Def7,Th6;
end;
end;

canceled;

theorem Th36:
for X being non empty Subset of ExtREAL holds
-infty is minorant of X
proof
let X be non empty Subset of ExtREAL;
for x being R_eal st x in X holds -infty <=' x by Def7,Th6;
hence thesis by Def10;
end;

canceled 2;

theorem Th39:
for X,Y being non empty Subset of ExtREAL holds
X c= Y implies
(for LB being R_eal holds LB is minorant of Y implies LB is minorant of X)
proof
let X,Y be non empty Subset of ExtREAL;
assume
A1:X c= Y;
let LB be R_eal;
assume LB is minorant of Y;
then for x be R_eal st x in X holds LB <=' x by A1,Def10;
hence thesis by Def10;
end;

definition
redefine func REAL -> non empty Subset of ExtREAL;
coherence by Def6,XBOOLE_1:7;
end;

canceled;

theorem
+infty is majorant of REAL by Th33;

theorem
-infty is minorant of REAL by Th36;

::
::       Bounded above, bounded below and bounded sets of r_eal numbers
::

definition
let X be non empty Subset of ExtREAL;
attr X is bounded_above means
:Def11: ex UB being majorant of X st UB in REAL;
end;

canceled;

theorem Th44:
for X,Y being non empty Subset of ExtREAL holds
X c= Y implies (Y is bounded_above implies X is bounded_above)
proof
let X,Y be non empty Subset of ExtREAL;
assume
A1:X c= Y;
assume Y is bounded_above;
then ex UB being majorant of Y st UB in REAL by Def11;
then consider UB being R_eal such that
A2:UB is majorant of Y & UB in REAL;
UB is majorant of X & UB in REAL by A1,A2,Th34;
hence thesis by Def11;
end;

theorem
not REAL is bounded_above
proof
for X being non empty Subset of ExtREAL holds
X = REAL implies not X is bounded_above
proof
let X be non empty Subset of ExtREAL;
assume
A1:X = REAL;
assume X is bounded_above;
then consider UB being majorant of X such that
A2:UB in REAL by Def11;
reconsider UB as Real by A2;
consider x being real number such that
A3:UB < x by REAL_1:76;
reconsider x as Real by XREAL_0:def 1;
reconsider x as R_eal by Def5,Def6;
reconsider UB as R_eal;
A4:x <=' UB by A1,Def9;
consider a,b being R_eal such that
A5:a = UB & b = x;
a <=' b by A3,A5,Def7;
hence thesis by A3,A4,A5,Th22;
end;
hence thesis;
end;

definition
let X be non empty Subset of ExtREAL;
attr X is bounded_below means
:Def12: ex LB being minorant of X st LB in REAL;
end;

canceled;

theorem Th47:
for X,Y being non empty Subset of ExtREAL holds
X c= Y implies (Y is bounded_below implies X is bounded_below)
proof
let X,Y be non empty Subset of ExtREAL;
assume
A1:X c= Y;
assume Y is bounded_below;
then ex LB being minorant of Y st LB in REAL by Def12;
then consider LB being R_eal such that
A2:LB is minorant of Y & LB in REAL;
LB is minorant of X & LB in REAL by A1,A2,Th39;
hence thesis by Def12;
end;

theorem
not REAL is bounded_below
proof
for X being non empty Subset of ExtREAL holds
X = REAL implies not X is bounded_below
proof
let X be non empty Subset of ExtREAL;
assume
A1:X = REAL;
assume X is bounded_below;
then consider LB being minorant of X such that
A2:LB in REAL by Def12;
reconsider LB as Real by A2;
consider x being real number such that
A3:x < LB by REAL_1:77;
reconsider x as Real by XREAL_0:def 1;
reconsider x as R_eal by Def5,Def6;
reconsider LB as R_eal;
A4:LB <=' x by A1,Def10;
consider a,b being R_eal such that
A5:a = x & b = LB;
a <=' b by A3,A5,Def7;
hence thesis by A3,A4,A5,Th22;
end;
hence thesis;
end;

definition
let X be non empty Subset of ExtREAL;
attr X is bounded means
:Def13:X is bounded_above bounded_below;
end;

canceled;

theorem
for X,Y being non empty Subset of ExtREAL holds
X c= Y implies (Y is bounded implies X is bounded)
proof
let X,Y be non empty Subset of ExtREAL;
assume
A1:X c= Y;
assume Y is bounded;
then Y is bounded_above & Y is bounded_below by Def13;
then X is bounded_above & X is bounded_below by A1,Th44,Th47;
hence thesis by Def13;
end;

theorem Th51:
for X being non empty Subset of ExtREAL holds
ex Y being non empty Subset of ExtREAL st
for x being R_eal holds x in Y iff x is majorant of X
proof
let X be non empty Subset of ExtREAL;
defpred P[R_eal] means \$1 is majorant of X;
ex Y being Subset of REAL \/ {-infty,+infty} st
for x being R_eal holds x in Y iff P[x] from SepR_eal;
then consider Y being Subset of REAL \/ {-infty,+infty} such that
A1:for x being R_eal holds x in Y iff x is majorant of X;
+infty is majorant of X by Th33;
then reconsider Y as non empty set by A1;
reconsider Y as non empty Subset of ExtREAL by Def6;
take Y;
thus thesis by A1;
end;

::
::       Set of majorant and set of minorant of X being SUBDOMAIN of ExtREAL
::

definition
let X be non empty Subset of ExtREAL;
func SetMajorant(X) -> Subset of ExtREAL means
:Def14: for x being R_eal holds x in it iff x is majorant of X;
existence
proof
consider Y being non empty Subset of ExtREAL such that
A1:   for x being R_eal holds x in Y iff x is majorant of X by Th51;
take Y;
thus thesis by A1;
end;
uniqueness
proof
let Y1,Y2 be Subset of ExtREAL such that
A2:for x being R_eal holds
x in Y1 iff x is majorant of X and
A3:for x being R_eal holds
x in Y2 iff x is majorant of X;
A4:for x being R_eal holds x in Y1 iff x in Y2
proof
let x be R_eal;
x in Y1 iff x is majorant of X by A2;
hence thesis by A3;
end;
thus Y1 c= Y2
proof
for x being set holds x in Y1 implies x in Y2 by A4;
hence thesis by TARSKI:def 3;
end;
thus Y2 c= Y1
proof
for x being set holds x in Y2 implies x in Y1 by A4;
hence thesis by TARSKI:def 3;
end;
end;
end;

definition
let X be non empty Subset of ExtREAL;
cluster SetMajorant(X) -> non empty;
coherence
proof
consider x being majorant of X;
x in SetMajorant(X) by Def14;
hence thesis;
end;
end;

canceled 2;

theorem
for X,Y being non empty Subset of ExtREAL holds
X c= Y implies
for x being R_eal holds (x in SetMajorant(Y) implies x in SetMajorant(X))
proof
let X,Y be non empty Subset of ExtREAL;
assume
A1:X c= Y;
let x be R_eal;
assume x in SetMajorant(Y);
then x is majorant of Y by Def14;
then x is majorant of X by A1,Th34;
hence thesis by Def14;
end;

theorem Th55:
for X being non empty Subset of ExtREAL holds
ex Y being non empty Subset of ExtREAL st
for x being R_eal holds x in Y iff x is minorant of X
proof
let X be non empty Subset of ExtREAL;
defpred P[R_eal] means \$1 is minorant of X;
ex Y being Subset of REAL \/ {-infty,+infty} st
for x being R_eal holds x in Y iff P[x] from SepR_eal;
then consider Y being Subset of REAL \/ {-infty,+infty} such that
A1:for x being R_eal holds x in Y iff x is minorant of X;
-infty is minorant of X by Th36;
then reconsider Y as non empty set by A1;
reconsider Y as non empty Subset of ExtREAL by Def6;
take Y;
thus thesis by A1;
end;

definition
let X be non empty Subset of ExtREAL;
func SetMinorant(X) -> Subset of ExtREAL means
:Def15: for x being R_eal holds x in it iff x is minorant of X;
existence
proof
consider Y being non empty Subset of ExtREAL such that
A1:  for x being R_eal holds x in Y iff x is minorant of X by Th55;
take Y;
thus thesis by A1;
end;
uniqueness
proof
let Y1,Y2 be Subset of ExtREAL such that
A2:for x being R_eal holds
x in Y1 iff x is minorant of X and
A3:for x being R_eal holds
x in Y2 iff x is minorant of X;
A4:for x being R_eal holds x in Y1 iff x in Y2
proof
let x be R_eal;
x in Y1 iff x is minorant of X by A2;
hence thesis by A3;
end;
thus Y1 c= Y2
proof
for x being set holds x in Y1 implies x in Y2 by A4;
hence thesis by TARSKI:def 3;
end;
thus Y2 c= Y1
proof
for x being set holds x in Y2 implies x in Y1 by A4;
hence thesis by TARSKI:def 3;
end;
end;
end;

definition
let X be non empty Subset of ExtREAL;
cluster SetMinorant(X) -> non empty;
coherence
proof
consider x being minorant of X;
x in SetMinorant(X) by Def15;
hence thesis;
end;
end;

canceled 2;

theorem
for X,Y being non empty Subset of ExtREAL holds
X c= Y implies
for x being R_eal holds (x in SetMinorant(Y) implies x in SetMinorant(X))
proof
let X,Y be non empty Subset of ExtREAL;
assume
A1:X c= Y;
let x be R_eal;
assume x in SetMinorant(Y);
then x is minorant of Y by Def15;
then x is minorant of X by A1,Th39;
hence thesis by Def15;
end;

theorem Th59:
for X being non empty Subset of ExtREAL holds
X is bounded_above & not X = {-infty} implies
ex x being Real st x in X & not x = -infty
proof
let X be non empty Subset of ExtREAL;
assume
A1:X is bounded_above & not X = {-infty};
ex x being set st x in X & not x = -infty
proof
assume
A2:   not ex x being set st x in X & not x = -infty;
for x being set holds x in X implies x in {-infty}
proof
let x be set;
assume x in X;
then x = -infty by A2;
hence thesis by TARSKI:def 1;
end;
then X c= {-infty} by TARSKI:def 3;
hence thesis by A1,ZFMISC_1:39;
end;
then consider x being set such that
A3:x in X & not x = -infty;
x in REAL
proof
A4:not x = +infty
proof
assume
A5:x = +infty;
then reconsider x as R_eal;
consider UB0 being majorant of X such that
A6:UB0 in REAL by A1,Def11;
reconsider UB0 as Real by A6;
reconsider UB0 as R_eal;
x <=' UB0 by A3,Def9;
hence thesis by A5,Th18;
end;
x in REAL or x in {-infty,+infty} by A3,Def6,XBOOLE_0:def 2;
hence thesis by A3,A4,TARSKI:def 2;
end;
then reconsider x as Real;
take x;
thus thesis by A3;
end;

theorem Th60:
for X being non empty Subset of ExtREAL holds
X is bounded_below & not X = {+infty} implies
ex x being Real st x in X & not x = +infty
proof
let X be non empty Subset of ExtREAL;
assume
A1:X is bounded_below & not X = {+infty};
ex x being set st x in X & not x = +infty
proof
assume
A2:   not ex x being set st x in X & not x = +infty;
for x being set holds x in X implies x in {+infty}
proof
let x be set;
assume x in X;
then x = +infty by A2;
hence thesis by TARSKI:def 1;
end;
then X c= {+infty} by TARSKI:def 3;
hence thesis by A1,ZFMISC_1:39;
end;
then consider x being set such that
A3:x in X & not x = +infty;
x in REAL
proof
A4:not x = -infty
proof
assume
A5:x = -infty;
then reconsider x as R_eal;
consider LB0 being minorant of X such that
A6:LB0 in REAL by A1,Def12;
reconsider LB0 as Real by A6;
reconsider LB0 as R_eal;
LB0 <=' x by A3,Def10;
hence thesis by A5,Th17;
end;
x in REAL or x in {-infty,+infty} by A3,Def6,XBOOLE_0:def 2;
hence thesis by A3,A4,TARSKI:def 2;
end;
then reconsider x as Real;
take x;
thus thesis by A3;
end;

canceled;

theorem Th62:
for X being non empty Subset of ExtREAL holds
(X is bounded_above & not X = {-infty}) implies
ex UB being R_eal st ((UB is majorant of X) &
(for y being R_eal holds
(y is majorant of X ) implies (UB <=' y)))
proof
let X be non empty Subset of ExtREAL;
assume
A1:X is bounded_above & not X = {-infty};
then consider UB0 being majorant of X such that
A2:UB0 in REAL by Def11;
A3:UB0 in SetMajorant(X) by Def14;
consider x being Real such that
A4:x in X & not x = -infty by A1,Th59;
reconsider S = X /\ REAL as Subset of REAL by XBOOLE_1:17;
reconsider Y = REAL /\ SetMajorant(X) as Subset of REAL by XBOOLE_1:17;
reconsider UB0 as Real by A2;
A5:x in S by A4,XBOOLE_0:def 3;
now let a,b be real number;
assume
A6:a in S & b in Y;
then A7:a in X by XBOOLE_0:def 3;
A8:b in SetMajorant(X) by A6,XBOOLE_0:def 3;
A9:  a is Real & b is Real by XREAL_0:def 1;
then reconsider d = b as R_eal by Def5,Def6;
A10:d is majorant of X by A8,Def14;
reconsider c = a as R_eal by A9,Def5,Def6;
c <=' d by A7,A10,Def9;
then ex p,q being Real st p = c & q = d & p <= q by A9,Def7;
hence a <= b;
end;
then consider UB being real number such that
A11:for a,b being real number st a in S & b in Y holds a <= UB & UB <= b by
AXIOMS:26;
set d = UB;
reconsider UB as Real by XREAL_0:def 1;
reconsider UB as R_eal by Def5,Def6;
A12:now let a,b be R_eal;
assume
A13:a in X & b in SetMajorant(X);
thus (a <=' UB & UB <=' b)
proof
A14:(not a = -infty & b = +infty) implies (a <=' UB & UB <=' b)
proof
assume
A15:not a = -infty & b = +infty;
a in REAL
proof
A16:a <> +infty
proof
assume
A17:a = +infty;
reconsider UB0 as R_eal;
a <=' UB0 by A13,Def9;
hence thesis by A17,Th18;
end;
a in REAL or a in {-infty,+infty} by Def6,XBOOLE_0:def 2;
hence thesis by A15,A16,TARSKI:def 2;
end;
then reconsider a as Real;
A18:a in S by A13,XBOOLE_0:def 3;
a <= d & d <= UB0
proof
UB0 in Y by A3,XBOOLE_0:def 3;
hence thesis by A11,A18;
end;
hence thesis by A15,Def7,Th2;
end;
A19:(a = -infty & not b = +infty) implies (a <=' UB & UB <=' b)
proof
assume
A20:a = -infty & b <> +infty;
A21:              b is majorant of X by A13,Def14;
reconsider x as R_eal by Def5,Def6;
x <=' b by A4,A21,Def9;
then A22:not b = -infty by Th17;
b in REAL or b in {-infty,+infty} by Def6,XBOOLE_0:def 2;
then reconsider b as Real by A20,A22,TARSKI:def 2;
A23:b in Y by A13,XBOOLE_0:def 3;
reconsider x as Real;
x <= d & d <= b by A5,A11,A23;
hence thesis by A20,Def7,Th6;
end;
(a <> -infty & b <> +infty) implies (a <=' UB & UB <=' b)
proof
assume
A24:a <> -infty & b <> +infty;
a in REAL
proof
A25:not a = +infty
proof
assume
A26:a = +infty;
reconsider UB0 as R_eal;
a <=' UB0 by A13,Def9;
hence thesis by A26,Th18;
end;
a in REAL or a in {-infty,+infty} by Def6,XBOOLE_0:def 2;
hence thesis by A24,A25,TARSKI:def 2;
end;
then reconsider a as Real;
A27:              b is majorant of X by A13,Def14;
reconsider x as R_eal by Def5,Def6;
x <=' b by A4,A27,Def9;
then A28:not b = -infty by Th17;
b in REAL or b in {-infty,+infty} by Def6,XBOOLE_0:def 2;
then reconsider b as Real by A24,A28,TARSKI:def 2;
A29:b in Y by A13,XBOOLE_0:def 3;
a in S by A13,XBOOLE_0:def 3;
then a <= d & d <= b by A11,A29;
hence thesis by Def7;
end;
hence thesis by A14,A19,Def7,Th2,Th6;
end;
end;
A30:UB is majorant of X
proof
for a being R_eal st a in X holds a <=' UB by A3,A12;
hence thesis by Def9;
end;
A31:for y being R_eal holds
(y is majorant of X ) implies (UB <=' y)
proof
let y be R_eal;
assume
y is majorant of X;
then y in SetMajorant(X) by Def14;
hence thesis by A4,A12;
end;
take UB;
thus thesis by A30,A31;
end;

theorem Th63:
for X being non empty Subset of ExtREAL holds
(X is bounded_below & not X = {+infty}) implies
ex LB being R_eal st ((LB is minorant of X) &
(for y being R_eal holds
(y is minorant of X ) implies (y <=' LB)))
proof
let X be non empty Subset of ExtREAL;
assume
A1:X is bounded_below & not X = {+infty};
then consider LB0 being minorant of X such that
A2:LB0 in REAL by Def12;
A3:LB0 in SetMinorant(X) by Def15;
consider x being Real such that
A4:x in X & not x = +infty by A1,Th60;
reconsider S = X /\ REAL as Subset of REAL by XBOOLE_1:17;
reconsider Y = REAL /\ SetMinorant(X) as Subset of REAL by XBOOLE_1:17;
reconsider LB0 as Real by A2;
A5:x in S by A4,XBOOLE_0:def 3;
now let b,a be real number;
assume
A6:b in Y & a in S;
then A7:a in X by XBOOLE_0:def 3;
A8:b in SetMinorant(X) by A6,XBOOLE_0:def 3;
A9: a is Real & b is Real by XREAL_0:def 1;
then reconsider d = b as R_eal by Def5,Def6;
A10:d is minorant of X by A8,Def15;
reconsider c = a as R_eal by A9,Def5,Def6;
d <=' c by A7,A10,Def10;
then ex p,q being Real st p = d & q = c & p <= q by A9,Def7;
hence b <= a;
end;
then consider LB being real number such that
A11:for b,a being real number st b in Y & a in S holds b <= LB & LB <= a by
AXIOMS:26;
reconsider LB as Real by XREAL_0:def 1;
set d = LB;
reconsider LB as R_eal by Def5,Def6;
A12:for b,a being R_eal st b in SetMinorant(X) & a in
X holds b <=' LB & LB <=' a
proof
let b,a be R_eal;
assume
A13:b in SetMinorant(X) & a in X;
A14:(b = -infty & a <> +infty) implies (b <=' LB & LB <=' a)
proof
assume
A15:b = -infty & not a = +infty;
a in REAL
proof
A16:a <> -infty
proof
assume
A17:a = -infty;
reconsider LB0 as R_eal;
LB0 <=' a by A13,Def10;
hence thesis by A17,Th17;
end;
a in REAL or a in {-infty,+infty} by Def6,XBOOLE_0:def 2;
hence thesis by A15,A16,TARSKI:def 2;
end;
then reconsider a as Real;
A18:a in S by A13,XBOOLE_0:def 3;
LB0 <= d & d <= a
proof
LB0 in Y by A3,XBOOLE_0:def 3;
hence thesis by A11,A18;
end;
hence thesis by A15,Def7,Th6;
end;
A19:(not b = -infty & a = +infty) implies (b <=' LB & LB <=' a)
proof
assume
A20:not b = -infty & a = +infty;
A21:       b is minorant of X by A13,Def15;
reconsider x as R_eal by Def5,Def6;
b <=' x by A4,A21,Def10;
then A22:not b = +infty by Th18;
b in REAL or b in {-infty,+infty} by Def6,XBOOLE_0:def 2;
then reconsider b as Real by A20,A22,TARSKI:def 2;
A23:b in Y by A13,XBOOLE_0:def 3;
reconsider x as Real;
b <= d & d <= x by A5,A11,A23;
hence thesis by A20,Def7,Th2;
end;
(not b = -infty & not a = +infty) implies (b <=' LB & LB <=' a)
proof
assume
A24:not b = -infty & not a = +infty;
a in REAL
proof
A25:not a = -infty
proof
assume
A26:a = -infty;
reconsider LB0 as R_eal;
LB0 <=' a by A13,Def10;
hence thesis by A26,Th17;
end;
a in REAL or a in {-infty,+infty} by Def6,XBOOLE_0:def 2;
hence thesis by A24,A25,TARSKI:def 2;
end;
then reconsider a as Real;
A27:              b is minorant of X by A13,Def15;
reconsider x as R_eal by Def5,Def6;
b <=' x by A4,A27,Def10;
then A28:not b = +infty by Th18;
b in REAL or b in {-infty,+infty} by Def6,XBOOLE_0:def 2;
then reconsider b as Real by A24,A28,TARSKI:def 2;
A29:b in Y by A13,XBOOLE_0:def 3;
a in S by A13,XBOOLE_0:def 3;
then b <= d & d <= a by A11,A29;
hence thesis by Def7;
end;
hence thesis by A14,A19,Def7,Th2,Th6;
end;
take LB;
for a being R_eal st a in X holds LB <=' a by A3,A12;
hence LB is minorant of X by Def10;
let y be R_eal;
assume
y is minorant of X;
then y in SetMinorant(X) by Def15;
hence thesis by A4,A12;
end;

theorem Th64:
for X being non empty Subset of ExtREAL holds
X = {-infty} implies X is bounded_above
proof
let X be non empty Subset of ExtREAL;
assume
A1:X = {-infty};
consider x being Element of REAL;
reconsider x as R_eal;
now let a be R_eal;
assume a in X;
then a = -infty by A1,TARSKI:def 1;
hence a <=' x by Def7,Th6;
end;
then x is majorant of X by Def9;
hence thesis by Def11;
end;

theorem Th65:
for X being non empty Subset of ExtREAL holds
X = {+infty} implies X is bounded_below
proof
let X be non empty Subset of ExtREAL;
assume
A1:X = {+infty};
consider x being Element of REAL;
reconsider x as R_eal;
now let a be R_eal;
assume a in X;
then a = +infty by A1,TARSKI:def 1;
hence x <=' a by Def7,Th2;
end;
then x is minorant of X by Def10;
hence thesis by Def12;
end;

theorem Th66:
for X being non empty Subset of ExtREAL holds
X = {-infty} implies
ex UB being R_eal st ((UB is majorant of X) &
(for y being R_eal holds
(y is majorant of X ) implies (UB <=' y)))
proof
let X be non empty Subset of ExtREAL;
assume
A1:X = {-infty};
set UB = -infty;
A2:for a being R_eal holds a in X implies a <=' UB by A1,TARSKI:def 1;
take UB;
thus thesis by A2,Def7,Def9,Th6;
end;

theorem Th67:
for X being non empty Subset of ExtREAL holds
X = {+infty} implies
ex LB being R_eal st ((LB is minorant of X) &
(for y being R_eal holds
(y is minorant of X ) implies (y <=' LB)))
proof
let X be non empty Subset of ExtREAL;
assume
A1:X = {+infty};
set LB = +infty;
A2:   for a being R_eal holds a in X implies LB <=' a by A1,TARSKI:def 1;
take LB;
thus thesis by A2,Def7,Def10,Th2;
end;

theorem Th68:
for X being non empty Subset of ExtREAL holds
X is bounded_above implies
ex UB being R_eal st ((UB is majorant of X) &
(for y being R_eal holds
y is majorant of X implies UB <=' y))
proof
let X be non empty Subset of ExtREAL;
assume X is bounded_above;
then (X is bounded_above & not X = {-infty}) or (X is bounded_above & X = {
-infty});
hence thesis by Th62,Th66;
end;

theorem Th69:
for X being non empty Subset of ExtREAL holds
X is bounded_below implies
ex LB being R_eal st ((LB is minorant of X) &
(for y being R_eal holds
(y is minorant of X ) implies (y <=' LB)))
proof
let X be non empty Subset of ExtREAL;
assume X is bounded_below;
then (X is bounded_below & not X = {+infty}) or (X is bounded_below & X = {
+infty});
hence thesis by Th63,Th67;
end;

theorem Th70:
for X being non empty Subset of ExtREAL holds
not X is bounded_above implies
(for y being R_eal holds
(y is majorant of X implies y = +infty))
proof
let X be non empty Subset of ExtREAL;
assume
A1:not X is bounded_above;
for y being R_eal holds
(y is majorant of X implies y = +infty)
proof
let y be R_eal;
assume
A2:y is majorant of X;
then not y in REAL by A1,Def11;
then A3: y in {-infty,+infty} by Def6,XBOOLE_0:def 2;

not y = -infty
proof
assume
A4:y = -infty;
for a being set holds a in X implies a in {-infty}
proof
let a be set;
assume
A5:a in X;
then a in REAL or a in {-infty,+infty} by Def6,XBOOLE_0:def 2;
then A6:a in REAL or a = -infty or a = +infty by TARSKI:def 2;
reconsider a as R_eal by A5;
a <=' -infty by A2,A4,A5,Def9;
hence thesis by A6,Def7,Th6,Th14,TARSKI:def 1;
end;
then X c= {-infty} by TARSKI:def 3;
then X = {} or X = {-infty} by ZFMISC_1:39;
hence thesis by A1,Th64;
end;
hence thesis by A3,TARSKI:def 2;
end;
hence thesis;
end;

theorem Th71:
for X being non empty Subset of ExtREAL holds
not X is bounded_below implies
(for y being R_eal holds
(y is minorant of X implies y = -infty))
proof
let X be non empty Subset of ExtREAL;
assume
A1:not X is bounded_below;

for y being R_eal holds
(y is minorant of X implies y = -infty)
proof
let y be R_eal;
assume
A2:y is minorant of X;
then not y in REAL by A1,Def12;
then A3: y in {-infty,+infty} by Def6,XBOOLE_0:def 2;
not y = +infty
proof
assume
A4:y = +infty;
for a being set holds a in X implies a in {+infty}
proof
let a be set;
assume
A5:a in X;

then a in REAL or a in {-infty,+infty} by Def6,XBOOLE_0:def 2;
then A6:a in REAL or a = -infty or a = +infty by TARSKI:def 2;
reconsider a as R_eal by A5;
+infty <=' a by A2,A4,A5,Def10;
hence thesis by A6,Def7,Th2,Th14,TARSKI:def 1;
end;
then X c= {+infty} by TARSKI:def 3;
then X = {} or X = {+infty} by ZFMISC_1:39;
hence thesis by A1,Th65;
end;
hence thesis by A3,TARSKI:def 2;
end;
hence thesis;
end;

theorem Th72:
for X being non empty Subset of ExtREAL holds
ex UB being R_eal st ((UB is majorant of X) &
(for y being R_eal holds
(y is majorant of X ) implies (UB <=' y)))
proof
let X be non empty Subset of ExtREAL;
not X is bounded_above implies
ex UB being R_eal st ((UB is majorant of X) &
(for y being R_eal holds
(y is majorant of X ) implies (UB <=' y)))
proof
assume
A1:   not X is bounded_above;
set UB = +infty;
take UB;
thus thesis by A1,Th33,Th70;
end;
hence thesis by Th68;
end;

theorem Th73:
for X being non empty Subset of ExtREAL holds
ex LB being R_eal st ((LB is minorant of X) &
(for y being R_eal holds
(y is minorant of X) implies (y <=' LB)))
proof
let X be non empty Subset of ExtREAL;
not X is bounded_below implies
ex LB being R_eal st ((LB is minorant of X) &
(for y being R_eal holds
(y is minorant of X ) implies (y <=' LB)))
proof
assume
A1:   not X is bounded_below;
set LB = -infty;
take LB;
thus thesis by A1,Th36,Th71;
end;
hence thesis by Th69;
end;

::
::       sup X, inf X least upper bound and greatest lower bound of set X
::

definition
let X be non empty Subset of ExtREAL;
func sup X -> R_eal means
:Def16: it is majorant of X &
for y being R_eal holds
y is majorant of X implies it <=' y;
existence by Th72;
uniqueness
proof
let S1,S2 be R_eal such that
A1:S1 is majorant of X &
for y being R_eal holds
(y is majorant of X ) implies (S1 <=' y) and
A2:S2 is majorant of X &
for y being R_eal holds
(y is majorant of X ) implies (S2 <=' y);
S1 <=' S2 & S2 <=' S1 by A1,A2;
hence thesis by Th22;
end;
end;

canceled 2;

theorem Th76:
for X being non empty Subset of ExtREAL holds
for x being R_eal holds
x in X implies x <=' sup X
proof
let X be non empty Subset of ExtREAL;
let x be R_eal;
assume
A1:x in X;
sup X is majorant of X by Def16;
hence thesis by A1,Def9;
end;

definition
let X be non empty Subset of ExtREAL;
func inf X -> R_eal means
:Def17: it is minorant of X &
for y being R_eal holds
y is minorant of X implies y <=' it;
existence by Th73;
uniqueness
proof
let S1,S2 be R_eal such that
A1:S1 is minorant of X &
for y being R_eal holds
(y is minorant of X ) implies (y <=' S1) and
A2:S2 is minorant of X &
for y being R_eal holds
(y is minorant of X ) implies (y <=' S2);
S1 <=' S2 & S2 <=' S1 by A1,A2;
hence thesis by Th22;
end;
end;

canceled 2;

theorem Th79:
for X being non empty Subset of ExtREAL holds
for x being R_eal holds
x in X implies inf X <=' x
proof
let X be non empty Subset of ExtREAL;
let x be R_eal;
assume
A1:x in X;
inf X is minorant of X by Def17;
hence thesis by A1,Def10;
end;

theorem Th80:
for X being non empty Subset of ExtREAL holds
for x being majorant of X holds
x in X implies x = sup X
proof
let X be non empty Subset of ExtREAL;
let x be majorant of X;
assume x in X;
then for y being R_eal holds
(y is majorant of X) implies (x <=' y) by Def9;
hence thesis by Def16;
end;

theorem Th81:
for X being non empty Subset of ExtREAL holds
for x being minorant of X holds
x in X implies x = inf X
proof
let X be non empty Subset of ExtREAL;
let x be minorant of X;
assume x in X;
then for y being R_eal holds
(y is minorant of X) implies (y <=' x) by Def10;
hence thesis by Def17;
end;

theorem
for X being non empty Subset of ExtREAL holds
sup X = inf SetMajorant(X) & inf X = sup SetMinorant(X)
proof
let X be non empty Subset of ExtREAL;
sup X is majorant of X by Def16;
then A1:sup X in SetMajorant(X) by Def14;
for y being R_eal holds (y in SetMajorant(X)) implies
sup X <=' y
proof
let y be R_eal;
assume y in SetMajorant(X);
then y is majorant of X by Def14;
hence thesis by Def16;
end;
then A2: sup X is minorant of SetMajorant(X) by Def10;
inf X is minorant of X by Def17;
then A3:inf X in SetMinorant(X) by Def15;
for y being R_eal holds (y in SetMinorant(X)) implies
(y <=' inf X)
proof
let y be R_eal;
assume y in SetMinorant(X);
then y is minorant of X by Def15;
hence thesis by Def17;
end;
then inf X is majorant of SetMinorant(X) by Def9;
hence thesis by A1,A2,A3,Th80,Th81;
end;

theorem
for X being non empty Subset of ExtREAL holds
X is bounded_above & not X = {-infty} implies sup X in REAL
proof
let X be non empty Subset of ExtREAL;
assume
A1:X is bounded_above & not X = {-infty};
then consider UB0 being majorant of X such that
A2:UB0 in REAL by Def11;
A3:sup X <=' UB0 by Def16;
consider x being Real such that
A4:x in X & not x = -infty by A1,Th59;
reconsider x as R_eal by Def5,Def6;
sup X is majorant of X by Def16;
then x <=' sup X by A4,Def9;
then not sup X = -infty by Th17;
hence thesis by A2,A3,Def7,Th2;
end;

theorem
for X being non empty Subset of ExtREAL holds
X is bounded_below & not X = {+infty} implies inf X in REAL
proof
let X be non empty Subset of ExtREAL;
assume
A1:X is bounded_below & not X = {+infty};
then consider LB0 being minorant of X such that
A2:LB0 in REAL by Def12;
A3:LB0 <=' inf X by Def17;
consider x being Real such that
A4:x in X & not x = +infty by A1,Th60;
reconsider x as R_eal by Def5,Def6;
inf X is minorant of X by Def17;
then inf X <=' x by A4,Def10;
then not inf X = +infty by Th18;
hence thesis by A2,A3,Def7,Th6;
end;

definition let x be R_eal;
redefine func {x} -> Subset of ExtREAL;
coherence by ZFMISC_1:37;
end;

definition let x,y be R_eal;
redefine func {x,y} -> Subset of ExtREAL;
coherence by ZFMISC_1:38;
end;

theorem Th85:
for x being R_eal holds sup{x} = x
proof
let x be R_eal;
A1:sup{x} is majorant of {x} by Def16;
x is majorant of {x}
proof
for a being R_eal holds a in {x} implies a <=' x by TARSKI:def 1;
hence thesis by Def9;
end;
then A2:sup{x} <=' x by Def16;
x in {x} by TARSKI:def 1;
then x <=' sup{x} by A1,Def9;
hence thesis by A2,Th22;
end;

theorem Th86:
for x being R_eal holds inf{x} = x
proof
let x be R_eal;
A1:inf{x} is minorant of {x} by Def17;
x is minorant of {x}
proof
for a being R_eal holds a in {x} implies x <=' a by TARSKI:def 1;
hence thesis by Def10;
end;
then A2:x <=' inf{x} by Def17;
x in {x} by TARSKI:def 1;
then inf{x} <=' x by A1,Def10;
hence thesis by A2,Th22;
end;

theorem
sup {-infty} = -infty by Th85;

theorem
sup {+infty} = +infty by Th85;

theorem
inf {-infty} = -infty by Th86;

theorem
inf {+infty} = +infty by Th86;

theorem Th91:
for X,Y being non empty Subset of ExtREAL holds
X c= Y implies sup X <=' sup Y
proof
let X,Y be non empty Subset of ExtREAL;
assume
A1:X c= Y;
set S2 = sup Y;
S2 is majorant of Y &
for y being R_eal holds
(y is majorant of Y implies (S2 <=' y)) by Def16;
then S2 is majorant of X by A1,Th34;
hence thesis by Def16;
end;

theorem Th92:
for x,y being R_eal holds
for a being R_eal holds
(x <=' a & y <=' a implies sup{x,y} <=' a)
proof
let x,y be R_eal;
let a be R_eal;
assume x <=' a & y <=' a;
then for c being R_eal holds c in {x,y} implies c <=' a by TARSKI:def 2;
then a is majorant of {x,y} by Def9;
hence thesis by Def16;
end;

theorem
for x,y being R_eal holds
(x <=' y implies sup{x,y} = y) & (y <=' x implies sup{x,y} = x)
proof
let x,y be R_eal;
thus x <=' y implies sup{x,y} = y
proof
assume x <=' y;
then A1:sup{x,y} <=' y by Th92;
A2:y in {x,y} by TARSKI:def 2;
sup{x,y} is majorant of {x,y} by Def16;
then y <=' sup{x,y} by A2,Def9;
hence thesis by A1,Th22;
end;
assume y <=' x;
then A3:sup{x,y} <=' x by Th92;
A4:x in {x,y} by TARSKI:def 2;
sup{x,y} is majorant of {x,y} by Def16;
then x <=' sup{x,y} by A4,Def9;
hence thesis by A3,Th22;
end;

theorem Th94:
for X,Y being non empty Subset of ExtREAL holds
X c= Y implies inf Y <=' inf X
proof
let X,Y be non empty Subset of ExtREAL;
assume
A1:X c= Y;
inf Y <=' inf X
proof
set S2 = inf Y;
S2 is minorant of Y &
for y being R_eal holds
(y is minorant of Y implies (y <=' S2)) by Def17;
then S2 is minorant of X by A1,Th39;
hence thesis by Def17;
end;
hence thesis;
end;

theorem Th95:
for x,y being R_eal holds
for a being R_eal holds
(a <=' x & a <=' y implies a <=' inf{x,y})
proof
let x,y be R_eal;
let a be R_eal;
assume a <=' x & a <=' y;
then for c being R_eal holds c in {x,y} implies a <=' c by TARSKI:def 2;
then a is minorant of {x,y} by Def10;
hence thesis by Def17;
end;

theorem
for x,y being R_eal holds
(x <=' y implies inf{x,y} = x) & (y <=' x implies inf{x,y} = y)
proof
let x,y be R_eal;
thus x <=' y implies inf{x,y} = x
proof
assume x <='y;
then A1:x <=' inf{x,y} by Th95;
A2:x in {x,y} by TARSKI:def 2;
inf{x,y} is minorant of {x,y} by Def17;
then inf{x,y} <=' x by A2,Def10;
hence thesis by A1,Th22;
end;
assume y <='x;
then A3:y <=' inf{x,y} by Th95;
A4:y in {x,y} by TARSKI:def 2;
inf{x,y} is minorant of {x,y} by Def17;
then inf{x,y} <=' y by A4,Def10;
hence thesis by A3,Th22;
end;

theorem Th97:
for X being non empty Subset of ExtREAL holds
for x being R_eal holds
((ex y being R_eal st (y in X & x <=' y)) implies x <=' sup X)
proof
let X be non empty Subset of ExtREAL;
let x be R_eal;
given y being R_eal such that
A1:y in X & x <=' y;
sup X is majorant of X by Def16;
then y <=' sup X by A1,Def9;
hence thesis by A1,Th29;
end;

theorem Th98:
for X being non empty Subset of ExtREAL holds
for x being R_eal holds
((ex y being R_eal st (y in X & y <=' x)) implies inf X <=' x)
proof
let X be non empty Subset of ExtREAL;
let x be R_eal;
given y being R_eal such that
A1:y in X & y <=' x;
inf X is minorant of X by Def17;
then inf X <=' y by A1,Def10;
hence thesis by A1,Th29;
end;

theorem
for X,Y being non empty Subset of ExtREAL holds
(for x being R_eal st x in X holds
(ex y being R_eal st y in Y & x <=' y)) implies
sup X <=' sup Y
proof
let X,Y be non empty Subset of ExtREAL;
assume
A1:for x being R_eal st x in X holds (ex y being R_eal st y in Y & x <=' y);
for x being R_eal st x in X holds x <=' sup Y
proof
let x be R_eal;
assume x in X;
then consider y being R_eal such that
A2:y in Y & x <=' y by A1;
y <=' sup Y by A2,Th76;
hence thesis by A2,Th29;
end;
then sup Y is majorant of X by Def9;
hence thesis by Def16;
end;

theorem
for X,Y being non empty Subset of ExtREAL holds
(for y being R_eal st y in Y holds
(ex x being R_eal st x in X & x <=' y)) implies
inf X <=' inf Y
proof
let X,Y be non empty Subset of ExtREAL;
assume
A1:for y being R_eal st y in Y holds (ex x being R_eal st x in X & x <=' y);
for y being R_eal st y in Y holds inf X <=' y
proof
let y be R_eal;
assume y in Y;
then consider x being R_eal such that
A2:x in X & x <=' y by A1;
inf X <=' x by A2,Th79;
hence thesis by A2,Th29;
end;
then inf X is minorant of Y by Def10;
hence thesis by Def17;
end;

theorem Th101:
for X,Y being non empty Subset of ExtREAL holds
for UB1 being majorant of X holds
for UB2 being majorant of Y holds
sup{UB1,UB2} is majorant of X \/ Y
proof
let X,Y be non empty Subset of ExtREAL;
let UB1 be majorant of X;
let UB2 be majorant of Y;
for a being R_eal holds
a in X \/ Y implies a <=' sup{UB1,UB2}
proof
let a be R_eal;
assume
A1:   a in X \/ Y;
A2:a in X implies a <=' sup{UB1,UB2}
proof
assume a in X;
then A3:a <=' UB1 by Def9;
A4:UB1 in {UB1,UB2} by TARSKI:def 2;
sup{UB1,UB2} is majorant of {UB1,UB2} by Def16;
then UB1 <=' sup{UB1,UB2}by A4,Def9;
hence thesis by A3,Th29;
end;
a in Y implies a <=' sup{UB1,UB2}
proof
assume a in Y;
then A5:a <=' UB2 by Def9;
A6:UB2 in {UB1,UB2} by TARSKI:def 2;
sup{UB1,UB2} is majorant of {UB1,UB2} by Def16;
then UB2 <=' sup{UB1,UB2}by A6,Def9;
hence thesis by A5,Th29;
end;
hence thesis by A1,A2,XBOOLE_0:def 2;
end;
hence thesis by Def9;
end;

theorem Th102:
for X,Y being non empty Subset of ExtREAL holds
for LB1 being minorant of X holds
for LB2 being minorant of Y holds
inf{LB1,LB2} is minorant of X \/ Y
proof
let X,Y be non empty Subset of ExtREAL;
let LB1 be minorant of X;
let LB2 be minorant of Y;
for a being R_eal holds
a in X \/ Y implies inf{LB1,LB2} <=' a
proof
let a be R_eal;
assume
A1:   a in X \/ Y;

A2:a in X implies inf{LB1,LB2} <=' a
proof
assume a in X;
then A3:LB1 <=' a by Def10;
A4:LB1 in {LB1,LB2} by TARSKI:def 2;
inf{LB1,LB2} is minorant of {LB1,LB2} by Def17;
then inf{LB1,LB2} <=' LB1 by A4,Def10;
hence thesis by A3,Th29;
end;
a in Y implies inf{LB1,LB2} <=' a
proof
assume a in Y;
then A5:LB2 <=' a by Def10;
A6:LB2 in {LB1,LB2} by TARSKI:def 2;
inf{LB1,LB2} is minorant of {LB1,LB2} by Def17;
then inf{LB1,LB2} <=' LB2 by A6,Def10;
hence thesis by A5,Th29;
end;
hence thesis by A1,A2,XBOOLE_0:def 2;
end;
hence thesis by Def10;
end;

theorem Th103:
for X,Y,S being non empty Subset of ExtREAL holds
for UB1 being majorant of X holds
for UB2 being majorant of Y holds
S = X /\ Y implies inf{UB1,UB2} is majorant of S
proof
let X,Y,S be non empty Subset of ExtREAL;
let UB1 be majorant of X;
let UB2 be majorant of Y;
assume
A1:S = X /\ Y;
now let a be R_eal;
assume a in S;
then a in X & a in Y by A1,XBOOLE_0:def 3;
then a <=' UB1 & a <=' UB2 by Def9;
hence a <=' inf{UB1,UB2} by Th95;
end;
hence thesis by Def9;
end;

theorem Th104:
for X,Y,S being non empty Subset of ExtREAL holds
for LB1 being minorant of X holds
for LB2 being minorant of Y holds
S = X /\ Y implies sup{LB1,LB2} is minorant of S
proof
let X,Y,S be non empty Subset of ExtREAL;
let LB1 be minorant of X;
let LB2 be minorant of Y;
assume
A1:S = X /\ Y;
now let a be R_eal;
assume a in S;
then a in X & a in Y by A1,XBOOLE_0:def 3;
then LB1 <=' a & LB2 <=' a by Def10;
hence sup{LB1,LB2} <=' a by Th92;
end;
hence thesis by Def10;
end;

theorem
for X,Y being non empty Subset of ExtREAL holds
sup(X \/ Y) = sup{sup X,sup Y}
proof
let X,Y be non empty Subset of ExtREAL;
set a = sup(X \/ Y);
A1:sup X is majorant of X by Def16;
sup Y is majorant of Y by Def16;
then sup{sup X,sup Y} is majorant of X \/ Y by A1,Th101;
then A2:a <=' sup{sup X,sup Y} by Def16;
X c= X \/ Y by XBOOLE_1:7;
then A3:sup X <=' a by Th91;
Y c= X \/ Y by XBOOLE_1:7;
then sup Y <=' a by Th91;
then sup{sup X,sup Y} <=' a by A3,Th92;
hence thesis by A2,Th22;
end;

theorem
for X,Y being non empty Subset of ExtREAL holds
inf(X \/ Y) = inf{inf X,inf Y}
proof
let X,Y be non empty Subset of ExtREAL;
set a = inf(X \/ Y);
A1:inf X is minorant of X by Def17;
inf Y is minorant of Y by Def17;
then inf{inf X,inf Y} is minorant of X \/ Y by A1,Th102;
then A2:inf{inf X,inf Y} <=' a by Def17;
X c= X \/ Y by XBOOLE_1:7;
then A3:a <=' inf X by Th94;
Y c= X \/ Y by XBOOLE_1:7;
then a <=' inf Y by Th94;
then a <=' inf{inf X,inf Y} by A3,Th95;
hence thesis by A2,Th22;
end;

theorem
for X,Y,S being non empty Subset of ExtREAL holds
S = X /\ Y implies sup(S) <=' inf{sup X,sup Y}
proof
let X,Y,S be non empty Subset of ExtREAL;
assume
A1:S = X /\ Y;
sup(S) <=' inf{sup X,sup Y}
proof
A2:sup X is majorant of X by Def16;
sup Y is majorant of Y by Def16;
then inf{sup X,sup Y} is majorant of S by A1,A2,Th103;
hence thesis by Def16;
end;
hence thesis;
end;

theorem
for X,Y,S being non empty Subset of ExtREAL holds
S = X /\ Y implies sup{inf X,inf Y} <=' inf(S)
proof
let X,Y,S be non empty Subset of ExtREAL;
assume
A1:S = X /\ Y;
sup{inf X,inf Y} <=' inf(S)
proof
A2:inf X is minorant of X by Def17;
inf Y is minorant of Y by Def17;
then sup{inf X,inf Y} is minorant of S by A1,A2,Th104;
hence thesis by Def17;
end;
hence thesis;
end;

definition
let X be non empty set;
mode bool_DOMAIN of X -> set means
:Def18: it is non empty Subset of bool X &
for A being set holds
A in it implies A is non empty set;
existence
proof
set F = {X};
A1: for x being set holds x in F implies x in bool X
proof
let x be set;
assume
A2:x in F;
X in bool X by ZFMISC_1:def 1;
hence thesis by A2,TARSKI:def 1;
end;
take F;
thus thesis by A1,TARSKI:def 1,def 3;
end;
end;

definition
let F be bool_DOMAIN of ExtREAL;
func SUP(F) -> Subset of ExtREAL means
:Def19:for a being R_eal holds
a in it iff ex A being non empty Subset of ExtREAL st
A in F & a = sup A;
existence
proof
defpred P[R_eal] means
ex A being non empty Subset of ExtREAL st A in F & \$1 = sup A;
ex S being Subset of REAL \/ {-infty,+infty} st
for a being R_eal holds a in S iff P[a] from SepR_eal;
then consider S being Subset of ExtREAL such that
A1:for a being R_eal holds a in S iff
ex A being non empty Subset of ExtREAL st (A in F & a = sup A) by Def6;
reconsider S as Subset of ExtREAL;
take S;
thus thesis by A1;
end;
uniqueness
proof
let S1,S2 be Subset of ExtREAL such that
A2:for a being R_eal holds a in S1 iff
ex A being non empty Subset of ExtREAL st (A in F & a = sup A) and
A3:for a being R_eal holds a in S2 iff
ex A being non empty Subset of ExtREAL st (A in F & a = sup A);
for a being set holds (a in S1 iff a in S2)
proof
let a be set;
hereby assume
a in S1;
then ex A being non empty Subset of ExtREAL st A in F & a = sup A by
A2;
hence a in S2 by A3;
end;
assume
A4:a in S2;
then reconsider a as R_eal;
ex A being non empty Subset of ExtREAL st A in F & a = sup A by A3,A4;
hence thesis by A2;
end;
hence thesis by TARSKI:2;
end;
end;

definition
let F be bool_DOMAIN of ExtREAL;
cluster SUP(F) -> non empty;
coherence
proof
A1:F is non empty Subset of bool ExtREAL &
for A being set holds A in F implies A is non empty set by Def18;
consider A being Element of F;
reconsider A as non empty Subset of ExtREAL by A1,TARSKI:def 3;
sup A = sup A;
hence thesis by A1,Def19;
end;
end;

canceled 3;

theorem Th112:
for F being bool_DOMAIN of ExtREAL holds
for S being non empty Subset of ExtREAL holds
S = union F implies sup S is majorant of SUP(F)
proof
let F be bool_DOMAIN of ExtREAL;
let S be non empty Subset of ExtREAL;
assume
A1:S = union F;
for x being R_eal holds x in SUP(F) implies x <=' sup S
proof
let x be R_eal;
assume x in SUP(F);
then consider A being non empty Subset of ExtREAL such that
A2:A in F & x = sup A by Def19;
A c= S
proof
let a be set; assume a in A;
hence thesis by A1,A2,TARSKI:def 4;
end;
hence thesis by A2,Th91;
end;
hence thesis by Def9;
end;

theorem Th113:
for F being bool_DOMAIN of ExtREAL holds
for S being non empty Subset of ExtREAL holds
S = union F implies sup SUP(F) is majorant of S
proof
let F be bool_DOMAIN of ExtREAL;
let S be non empty Subset of ExtREAL;
assume
A1:S = union F;
for x being R_eal holds
x in S implies x <=' sup SUP(F)
proof
let x be R_eal;
assume
x in S;
then consider Z being set such that
A2:x in Z & Z in F by A1,TARSKI:def 4;
F is non empty Subset of bool ExtREAL by Def18;
then reconsider Z as non empty Subset of ExtREAL by A2;
consider a being set such that
A3:a = sup Z;
reconsider a as R_eal by A3;
sup Z is majorant of Z by Def16;
then A4:x <=' sup Z by A2,Def9;
a in SUP(F) by A2,A3,Def19;
hence thesis by A3,A4,Th97;
end;
hence thesis by Def9;
end;

theorem
for F being bool_DOMAIN of ExtREAL holds
for S being non empty Subset of ExtREAL holds
S = union F implies sup S = sup SUP(F)
proof
let F be bool_DOMAIN of ExtREAL;
let S be non empty Subset of ExtREAL;
assume
A1:S = union F;
set a = sup S;
set b = sup SUP(F);
A2:sup SUP(F) is majorant of S by A1,Th113;
sup S is majorant of SUP(F) by A1,Th112;
then a <=' b & b <=' a by A2,Def16;
hence thesis by Th22;
end;

definition
let F be bool_DOMAIN of ExtREAL;
func INF(F) -> Subset of ExtREAL means
:Def20:for a being R_eal holds
a in it iff ex A being non empty Subset of ExtREAL st A in
F & a = inf A;
existence
proof defpred P[R_eal] means
ex A being non empty Subset of ExtREAL st A in F & \$1 = inf A;
A1:ex S being Subset of REAL \/ {-infty,+infty} st
for a being R_eal holds a in S iff P[a] from SepR_eal;
A2:F is non empty Subset of bool ExtREAL &
for A being set holds A in F implies A is non empty set by Def18;
consider A being Element of F;
reconsider A as non empty Subset of ExtREAL by A2,TARSKI:def 3;
A3:inf A = inf A;
consider S being Subset of ExtREAL such that
A4:for a being R_eal holds a in S iff
ex A being non empty Subset of ExtREAL st (A in F & a = inf A) by A1,Def6;
reconsider S as non empty set by A2,A3,A4;
reconsider S as non empty Subset of ExtREAL;
take S;
thus thesis by A4;
end;
uniqueness
proof
let S1,S2 be Subset of ExtREAL such that
A5:for a being R_eal holds a in S1 iff
ex A being non empty Subset of ExtREAL st (A in F & a = inf A) and
A6:for a being R_eal holds a in S2 iff
ex A being non empty Subset of ExtREAL st (A in F & a = inf A);
for a being set holds a in S1 iff a in S2
proof
let a be set;
hereby assume
A7:a in S1;
then reconsider a' = a as R_eal;
ex A being non empty Subset of ExtREAL st A in
F & a' = inf A by A5,A7;
hence a in S2 by A6;
end;
assume
A8:a in S2;
then reconsider a as R_eal;
ex A being non empty Subset of ExtREAL st A in F & a = inf A by A6,
A8
;
hence thesis by A5;
end;
hence thesis by TARSKI:2;
end;
end;

definition
let F be bool_DOMAIN of ExtREAL;
cluster INF(F) -> non empty;
coherence
proof
A1:F is non empty Subset of bool ExtREAL &
for A being set holds A in F implies A is non empty set by Def18;
consider A being Element of F;
reconsider A as non empty Subset of ExtREAL by A1,TARSKI:def 3;
inf A = inf A;
hence thesis by A1,Def20;
end;
end;

canceled 2;

theorem Th117:
for F being bool_DOMAIN of ExtREAL holds
for S being non empty Subset of ExtREAL holds
S = union F implies inf S is minorant of INF(F)
proof
let F be bool_DOMAIN of ExtREAL;
let S be non empty Subset of ExtREAL;
assume
A1:S = union F;
for x being R_eal holds x in INF(F) implies inf S <=' x
proof
let x be R_eal;
assume x in INF(F);
then consider A being non empty Subset of ExtREAL such that
A2:A in F & x = inf A by Def20;
A c= S
proof
let a be set; assume a in A;
hence thesis by A1,A2,TARSKI:def 4;
end;
hence thesis by A2,Th94;
end;
hence thesis by Def10;
end;

theorem Th118:
for F being bool_DOMAIN of ExtREAL holds
for S being non empty Subset of ExtREAL holds
S = union F implies inf INF(F) is minorant of S
proof
let F be bool_DOMAIN of ExtREAL;
let S be non empty Subset of ExtREAL;
assume
A1:S = union F;
for x being R_eal holds
x in S implies inf INF(F) <=' x
proof
let x be R_eal;
assume
x in S;
then consider Z being set such that
A2:x in Z & Z in F by A1,TARSKI:def 4;
F is non empty Subset of bool ExtREAL by Def18;
then reconsider Z as non empty Subset of ExtREAL by A2;
consider a being set such that
A3:a = inf Z;
reconsider a as R_eal by A3;
inf Z is minorant of Z by Def17;
then A4:inf Z <=' x by A2,Def10;
a in INF(F) by A2,A3,Def20;
hence thesis by A3,A4,Th98;
end;
hence thesis by Def10;
end;

theorem
for F being bool_DOMAIN of ExtREAL holds
for S being non empty Subset of ExtREAL holds
S = union F implies inf S = inf INF(F)
proof
let F be bool_DOMAIN of ExtREAL;
let S be non empty Subset of ExtREAL;
assume
A1:S = union F;
set a = inf S;
set b = inf INF(F);
A2:   inf INF(F) is minorant of S by A1,Th118;
inf S is minorant of INF(F) by A1,Th117;
then a <=' b & b <=' a by A2,Def17;
hence thesis by Th22;
end;
```