### Basic Properties of Extended Real Numbers

by
Noboru Endou,
Katsumi Wasaki, and
Yasunari Shidama

Copyright (c) 2000 Association of Mizar Users

MML identifier: EXTREAL1
[ MML identifier index ]

environ

vocabulary SUPINF_1, MEASURE6, ARYTM_3, ARYTM_1, RLVECT_1, ARYTM, COMPLEX1;
notation ORDINAL1, XCMPLX_0, XREAL_0, REAL_1, SUPINF_1, SUPINF_2, MEASURE6;
constructors REAL_1, SUPINF_2, MEASURE6, MEMBERED;
clusters XREAL_0, MEMBERED, XBOOLE_0;
requirements NUMERALS, REAL, SUBSET, BOOLE, ARITHM;
theorems TARSKI, SUPINF_1, MEASURE5, MEASURE6, REAL_1, REAL_2, SUPINF_2,
AXIOMS, MEASURE3, SQUARE_1, HAHNBAN, XBOOLE_0, XCMPLX_0, XCMPLX_1;

begin

reserve x,y,z for R_eal;
reserve a for Real;

theorem Th1:
x <> +infty & x <> -infty implies x is Real
proof
assume A1:x <> +infty & x <> -infty;
x in REAL or x in {-infty,+infty} by SUPINF_1:def 6,XBOOLE_0:def 2;
hence thesis by A1,TARSKI:def 2;
end;

theorem Th2:
-infty <' +infty
proof
consider a being Real;
a in REAL;
then R_EAL a in REAL by MEASURE6:def 1;
then -infty <' R_EAL a & R_EAL a <' +infty by SUPINF_1:31;
hence thesis by SUPINF_1:29;
end;

theorem Th3:
x <' y implies x <> +infty & y <> -infty
proof
assume A1:x <' y;
now
thus x <> +infty by A1,SUPINF_1:20;
thus y <> -infty by A1,SUPINF_1:21;
end;
hence thesis;
end;

theorem Th4:
(x = +infty iff -x = -infty) & (x = -infty iff -x = +infty)
proof
-x = +infty implies x = -infty
proof
assume -x = +infty;
then --x = -infty by SUPINF_2:def 3;
hence thesis;
end;
hence thesis by SUPINF_2:4;
end;

theorem Th5:
x - -y = x + y
proof
thus x - -y = x + - -y by SUPINF_2:def 4
.= x + y;
end;

canceled;

theorem Th7:
x <> -infty & y <> +infty & x <=' y implies x <> +infty & y <> -infty
proof
assume A1:x <> -infty & y <> +infty & x <=' y;
assume A2:not (x <> +infty & y <> -infty);
now per cases by A2;
suppose x = +infty;
suppose y = -infty;
end;
hence thesis;
end;

Lm1:
x in REAL implies x + -infty = -infty & x + +infty = +infty
proof
assume x in REAL;
hence thesis by SUPINF_1:2,6,SUPINF_2:def 2;
end;

Lm2:
x in REAL & y in REAL implies x + y in REAL
proof
assume x in REAL & y in REAL;
then consider a,b being Real such that
A1: x = a & y = b & x + y = a + b by SUPINF_2:def 2;
thus thesis by A1;
end;

theorem Th8:
not (x = +infty & y = -infty) & not (x = -infty & y = +infty) &
not ((y = +infty & z = -infty) or (y = -infty & z = +infty)) &
not ((x = +infty & z = -infty) or (x = -infty & z = +infty)) implies
x + y + z = x + (y + z)
proof
assume that
A1:not (x = +infty & y = -infty or x = -infty & y = +infty) and
A2:not ((y = +infty & z = -infty) or (y = -infty & z = +infty)) and
A3:not ((x = +infty & z = -infty) or (x = -infty & z = +infty));
now per cases by A1,A2,A3,SUPINF_2:2;
suppose x in REAL & y in REAL & z in REAL;
then reconsider A = x, B = y, C = z as Real;
A + B = x + y & B + C = y + z by SUPINF_2:1;
then A + B + C = x + y + z & A + (B + C) = x + (y + z) by SUPINF_2:1;
hence thesis by XCMPLX_1:1;
suppose A4: x in REAL & y = +infty & z in REAL;
then x + y = +infty & y + z = +infty by Lm1;
hence thesis by A4;
suppose A5: x in REAL & y = -infty & z in REAL;
then x + y = -infty & y + z = -infty by Lm1;
hence thesis by A5;
suppose A6: x = -infty & y in REAL & z in REAL;
then x + y = -infty by SUPINF_1:2,SUPINF_2:def 2;
then A7:   x + y + z = -infty by A6,SUPINF_1:2,SUPINF_2:def 2;
ex a,b being Real st y = a & z = b & y + z = a + b
by A6,SUPINF_2:def 2;
then y + z <> +infty by SUPINF_1:2;
hence thesis by A6,A7,SUPINF_2:def 2;

suppose A8: x = +infty & y in REAL & z in REAL;
then x + y = +infty by SUPINF_1:6,SUPINF_2:def 2;
then A9:   x + y + z = +infty by A8,SUPINF_1:6,SUPINF_2:def 2;
ex a,b being Real st y = a & z = b & y + z = a + b
by A8,SUPINF_2:def 2;
then y + z <> -infty by SUPINF_1:6;
hence thesis by A8,A9,SUPINF_2:def 2;

suppose A10: x in REAL & y in REAL & z = +infty;
then y + z = +infty by Lm1;
then A11:   x + (y + z) = +infty by A10,SUPINF_1:6,SUPINF_2:def 2;
x + y in REAL by A10,Lm2;
hence thesis by A10,A11,SUPINF_1:6,SUPINF_2:def 2;

suppose A12: x in REAL & y in REAL & z = -infty;
then y + z = -infty by Lm1;
then A13:   x + (y + z) = -infty by A12,SUPINF_1:2,SUPINF_2:def 2;
x + y in REAL by A12,Lm2;
hence thesis by A12,A13,SUPINF_1:2,SUPINF_2:def 2;

suppose A14: x = +infty & y = +infty & z in REAL;
then x + y = +infty by SUPINF_1:14,SUPINF_2:def 2;
then A15:   x + y + z = +infty by A14,SUPINF_1:6,SUPINF_2:def 2;
y + z <> -infty by A14,Lm1,SUPINF_1:14;
hence thesis by A14,A15,SUPINF_2:def 2;
suppose A16: x in REAL & y = -infty & z = -infty;
then A17:   x + y = -infty by SUPINF_1:2,SUPINF_2:def 2;
then x + y + z = -infty by A16,SUPINF_1:14,SUPINF_2:def 2;
hence thesis by A16,A17;
suppose A18: x = -infty & y = -infty & z in REAL;
then A19:   x + y = -infty by SUPINF_2:19,def 2;
then x + y + z = -infty by A18,SUPINF_1:2,SUPINF_2:def 2;
hence thesis by A18,A19;
suppose x = -infty & y in REAL & z = -infty or
x = -infty & y = -infty & z = -infty or
x = +infty & y in REAL & z = +infty or
x = +infty & y = +infty & z = +infty;
hence thesis;

suppose A20: x in REAL & y = +infty & z = +infty;
then x + y = +infty & y + z = +infty by Lm1,SUPINF_1:14,SUPINF_2:def 2;
hence thesis by A20;
end;
hence thesis;
end;

theorem Th9:
x + -x = 0.
proof
per cases by SUPINF_2:2;
suppose x in REAL;
then consider a being Real such that
A1:x = a & -x = -a by SUPINF_2:def 3;
x + -x = a + -a & -x + x = -a + a by A1,SUPINF_2:1;
hence thesis by SUPINF_2:def 1,XCMPLX_0:def 6;
suppose x = -infty;
hence thesis by SUPINF_1:6,14,SUPINF_2:4,def 2;
suppose x = +infty;
hence thesis by SUPINF_1:6,14,SUPINF_2:4,def 2;
end;

canceled;

theorem
not (x = +infty & y = -infty) & not (x = -infty & y = +infty) &
not (y = +infty & z = +infty) & not (y = -infty & z = -infty) &
not (x = +infty & z = +infty) & not (x = -infty & z = -infty) implies
x + y - z = x + (y - z)
proof
assume A1: not (x = +infty & y = -infty) & not (x = -infty & y = +infty) &
not (y = +infty & z = +infty) & not (y = -infty & z = -infty) &
not (x = +infty & z = +infty) & not (x = -infty & z = -infty);
then A2:not (y = +infty & -z = -infty) & not (y = -infty & -z = +infty) &
not (x = +infty & -z = -infty) & not (x = -infty & -z = +infty) by Th4;
thus x + y - z = x + y + -z by SUPINF_2:def 4
.= x + (y + -z) by A1,A2,Th8
.= x + (y - z) by SUPINF_2:def 4;
end;

begin  :: Operations "x * y","x / y", "|.x.|" in R_eal numbers

definition
let x,y be R_eal;
func x * y -> R_eal means :Def1:
(ex a,b being Real st (x = a & y = b & it = a * b)) or
(((0. <' x & y=+infty) or (0. <' y & x=+infty) or (x <' 0. & y=-infty) or
(y <' 0. & x = -infty)) & it = +infty) or
(((x <' 0. & y=+infty) or (y <' 0. & x=+infty) or (0. <' x & y=-infty) or
(0. <' y & x = -infty)) & it = -infty) or
((x = 0. or y = 0.) & it = 0.);
existence
proof
(x in REAL or x in {-infty,+infty}) & (y in REAL or y in {-infty,+infty})
by SUPINF_1:def 6,XBOOLE_0:def 2;
then A1:(x in REAL & y in REAL) or (0. <' x & y = +infty) or
(0. <' y & x = +infty) or (x <' 0. & y = +infty) or
(y <' 0. & x = +infty) or (0. <' x & y = -infty) or
(0. <' y & x = -infty) or (x <' 0. & y = -infty) or
(y <' 0. & x = -infty) or (x = 0.) or (y = 0.)
by SUPINF_1:22,TARSKI:def 2;
ex Z being R_eal st
((ex a,b being Real st (x = a & y = b & Z = a * b)) or
(((0. <' x & y = +infty) or (0. <' y & x = +infty)) & Z = +infty) or
(((x <' 0. & y = +infty) or (y <' 0. & x = +infty)) & Z = -infty) or
(((0. <' x & y = -infty) or (0. <' y & x = -infty)) & Z = -infty) or
(((x <' 0. & y = -infty) or (y <' 0. & x = -infty)) & Z = +infty) or
((x = 0. or y = 0.) & Z = 0.))
proof
x in REAL & y in REAL implies ex Z being R_eal st
(ex a,b being Real st (x = a & y = b & Z = a * b))
proof
assume x in REAL & y in REAL;
then reconsider x,y as Real;
reconsider Z = x * y as R_eal by SUPINF_1:10;
take Z;
thus thesis;
end;
hence thesis by A1;
end;
hence thesis;
end;
uniqueness by SUPINF_1:31,SUPINF_2:def 1;
end;

canceled;

theorem Th13:
for x,y being R_eal holds
for a,b being Real holds
(x = a & y = b) implies x * y = a * b
proof
let x,y be R_eal;
let a,b be Real;
assume A1:x = a & y = b;
then A2: -infty <' x & x <' +infty & -infty <' y & y <' +infty by SUPINF_1:31;
now per cases by A2,Def1;
suppose (ex a,b being Real st (x = a & y = b & x * y = a * b));
then consider a1,b1 being Real such that
A3:  x = a1 & y = b1 & x * y = a1 * b1;
thus thesis by A1,A3;
suppose ((x = 0. or y = 0.) & x * y = 0.);
hence thesis by A1,SUPINF_2:def 1;
end;
hence thesis;
end;

canceled 3;

theorem Th17:
for x,y being R_eal holds x * y = y * x
proof
let x,y be R_eal;
now per cases by Def1;
suppose
ex a,b being Real st (x = a & y = b & x * y = a * b);
then consider a1,b1 being Real such that
A1: x = a1 & y = b1 & x * y = a1 * b1;
thus thesis by A1,Def1;
suppose
((0. <' x & y=+infty) or (0. <' y & x=+infty) or (x <' 0. & y=-infty) or
(y <' 0. & x = -infty)) & x * y = +infty;
hence thesis by Def1;
suppose
((x <' 0. & y=+infty) or (y <' 0. & x=+infty) or (0. <' x & y=-infty) or
(0. <' y & x = -infty)) & x * y = -infty;
hence thesis by Def1;
suppose (x = 0. or y = 0.) & x * y = 0.;
hence thesis by Def1;
end;
hence thesis;
end;

definition let x,y be R_eal;
redefine func x*y;
commutativity by Th17;
end;

Lm3:
x = a & 0 < a implies 0. <' x
proof
assume that A1:x = a and A2:0 < a;
0. <=' x & x <> 0. by A1,A2,SUPINF_1:16,SUPINF_2:def 1;
hence thesis by SUPINF_1:22;
end;

Lm4:
x = a & a < 0 implies x <' 0.
proof
assume that A1:x = a and A2:a < 0;
x <=' 0. & x <> 0. by A1,A2,SUPINF_1:16,SUPINF_2:def 1;
hence thesis by SUPINF_1:22;
end;

theorem
x = a implies (0 < a iff 0. <' x) by Lm3,SUPINF_1:16,SUPINF_2:def 1;

theorem
x = a implies (a < 0 iff x <' 0.) by Lm4,SUPINF_1:16,SUPINF_2:def 1;

theorem Th20:
(0. <' x & 0. <' y) or (x <' 0. & y <' 0.) implies 0. <' x * y
proof
assume A1:(0. <' x & 0. <' y) or (x <' 0. & y <' 0.);
now per cases by A1;
suppose A2:0. <' x & 0. <' y;
now per cases by A2,Def1,SUPINF_2:19;
suppose ex a,b being Real st (x = a & y = b & x * y = a * b);
then consider a,b being Real such that
A3:  x = a & y = b & x * y = a * b;
0 < a & 0 < b by A2,A3,SUPINF_1:16,SUPINF_2:def 1;
then 0 < a * b by REAL_2:122;
hence thesis by A3,Lm3;
suppose ((0. <' x & y=+infty) or (0. <' y & x=+infty)) & x * y = +infty;
hence thesis by SUPINF_2:19;
end;
hence thesis;
suppose A4:x <' 0. & y <' 0.;
now per cases by A4,Def1,SUPINF_2:19;
suppose ex a,b being Real st (x = a & y = b & x * y = a * b);
then consider a,b being Real such that
A5:  x = a & y = b & x * y = a * b;
a < 0 & b < 0 by A4,A5,SUPINF_1:16,SUPINF_2:def 1;
then 0 < a * b by REAL_2:122;
hence thesis by A5,Lm3;
suppose ((x <' 0. & y=-infty) or (y <' 0. & x=-infty)) & x * y = +infty;
hence thesis by SUPINF_2:19;
end;
hence thesis;
end;
hence thesis;
end;

theorem Th21:
(0. <' x & y <' 0.) or (x <' 0. & 0. <' y) implies x * y <' 0.
proof
assume A1:(0. <' x & y <' 0.) or (x <' 0. & 0. <' y);
now per cases by A1;
suppose A2:0. <' x & y <' 0.;
now per cases by A2,Def1,SUPINF_2:19;
suppose ex a,b being Real st (x = a & y = b & x * y = a * b);
then consider a,b being Real such that
A3:  x = a & y = b & x * y = a * b;
0 < a & b < 0 by A2,A3,SUPINF_1:16,SUPINF_2:def 1;
then a * b < 0 by SQUARE_1:24;
hence thesis by A3,Lm4;
suppose ((0. <' x & y=-infty) or (y <' 0. & x=+infty)) & x * y = -infty;
hence thesis by SUPINF_2:19;
end;
hence thesis;
suppose A4:x <' 0. & 0. <' y;
now per cases by A4,Def1,SUPINF_2:19;
suppose ex a,b being Real st (x = a & y = b & x * y = a * b);
then consider a,b being Real such that
A5:  x = a & y = b & x * y = a * b;
a < 0 & 0 < b by A4,A5,SUPINF_1:16,SUPINF_2:def 1;
then a * b < 0 by SQUARE_1:24;
hence thesis by A5,Lm4;
suppose ((x <' 0. & y=+infty) or (0. <' y & x=-infty)) & x * y = -infty;
hence thesis by SUPINF_2:19;
end;
hence thesis;
end;
hence thesis;
end;

theorem
x * y = 0. iff (x = 0. or y = 0.)
proof
x * y = 0. implies (x = 0. or y = 0.)
proof
assume A1:x * y = 0.;
assume A2:x <> 0. & y <> 0.;
now per cases by A2,SUPINF_1:22;
suppose (x <' 0. & y <' 0.) or (0. <' x & 0. <' y);
suppose (x <' 0. & 0. <' y) or (0. <' x & y <' 0.);
end;
hence thesis;
end;
hence thesis by Def1;
end;

theorem
x*y*z = x*(y*z)
proof
now per cases by Def1;
suppose ex a,b being Real st (x = a & y = b & x * y = a * b);
then consider a,b being Real such that
A1: x = a & y = b & x * y = a * b;
A2: y <> +infty & y <> -infty by A1,SUPINF_1:31;
now per cases by A2,Def1;
suppose ex b1,c being Real st (y = b1 & z = c & y * z = b1 * c);
then consider b1,c being Real such that
A3:  y = b1 & z = c & y * z = b1 * c;
A4:  x * y * z = a * b * c by A1,A3,Th13;
x * (y * z) = a * (b * c) by A1,A3,Th13;
hence thesis by A4,XCMPLX_1:4;

suppose A5:0. <' y & z=+infty & y * z = +infty;
then A6:  b > 0 by A1,SUPINF_1:16,SUPINF_2:def 1;

now per cases;
suppose A7:a > 0;
then a * b > 0 by A6,REAL_2:122;
then 0. <' x * y by A1,Lm3;
then A8:  x * y * z = +infty by A5,Def1;
0. <' x by A1,A7,Lm3;
hence thesis by A5,A8,Def1;
suppose A9:a = 0;
then x * y * z = 0. by A1,Def1,SUPINF_2:def 1;
hence thesis by A1,A9,Def1,SUPINF_2:def 1;
suppose A10:a < 0;
then a * b < 0 by A6,SQUARE_1:24;
then x * y <' 0. by A1,Lm4;
then A11:  x * y * z = -infty by A5,Def1;
x <' 0. by A1,A10,Lm4;
hence thesis by A5,A11,Def1;
end;
hence thesis;

suppose A12:y <' 0. & z=-infty & y * z = +infty;
then A13: b < 0 by A1,SUPINF_1:16,SUPINF_2:def 1;
now per cases;
suppose A14:a > 0;
then a * b < 0 by A13,SQUARE_1:24;
then x * y <' 0. by A1,Lm4;
then A15:  x * y * z = +infty by A12,Def1;
0. <' x by A1,A14,Lm3;
hence thesis by A12,A15,Def1;
suppose A16:a = 0;
then x * y * z = 0. by A1,Def1,SUPINF_2:def 1;
hence thesis by A1,A16,Def1,SUPINF_2:def 1;
suppose A17:a < 0;
then a * b > 0 by A13,REAL_2:122;
then 0. <' x * y by A1,Lm3;
then A18:  x * y * z = -infty by A12,Def1;
x <' 0. by A1,A17,Lm4;
hence thesis by A12,A18,Def1;
end;
hence thesis;

suppose A19:y <' 0. & z=+infty & y * z = -infty;
then A20: b < 0 by A1,SUPINF_1:16,SUPINF_2:def 1;
now per cases;
suppose A21:a > 0;
then a * b < 0 by A20,SQUARE_1:24;
then x * y <' 0. by A1,Lm4;
then A22:  x * y * z = -infty by A19,Def1;
0. <' x by A1,A21,Lm3;
hence thesis by A19,A22,Def1;
suppose A23:a = 0;
then x * y * z = 0. by A1,Def1,SUPINF_2:def 1;
hence thesis by A1,A23,Def1,SUPINF_2:def 1;
suppose A24:a < 0;
then a * b > 0 by A20,REAL_2:122;
then 0. <' x * y by A1,Lm3;
then A25:  x * y * z = +infty by A19,Def1;
x <' 0. by A1,A24,Lm4;
hence thesis by A19,A25,Def1;
end;
hence thesis;
suppose A26:0. <' y & z=-infty & y * z = -infty;
then A27: 0 < b by A1,SUPINF_1:16,SUPINF_2:def 1;
now per cases;
suppose A28:a > 0;
then a * b > 0 by A27,REAL_2:122;
then 0. <' x * y by A1,Lm3;
then A29:  x * y * z = -infty by A26,Def1;
0. <' x by A1,A28,Lm3;
hence thesis by A26,A29,Def1;
suppose A30:a = 0;
then x * y * z = 0. by A1,Def1,SUPINF_2:def 1;
hence thesis by A1,A30,Def1,SUPINF_2:def 1;
suppose A31:a < 0;
then a * b < 0 by A27,SQUARE_1:24;
then x * y <' 0. by A1,Lm4;
then A32:  x * y * z = +infty by A26,Def1;
x <' 0. by A1,A31,Lm4;
hence thesis by A26,A32,Def1;
end;
hence thesis;
suppose A33:y = 0. & y * z = 0.;
then x * y * z = 0. by Def1;
hence thesis by A33,Def1;
suppose A34:z = 0. & y * z = 0.;
then x * y * z = 0. by Def1;
hence thesis by A34,Def1;
end;
hence thesis;

suppose A35:0. <' x & y=+infty & x * y = +infty;
now per cases by SUPINF_1:22;
suppose 0. <' z;
then y * z = +infty by A35,Def1;
hence thesis by A35;
suppose A36:0. = z;
then A37: x * y * z = 0. by Def1;
y * z = 0. by A36,Def1;
hence thesis by A37,Def1;
suppose z <' 0.;
then y * z = -infty by A35,Def1;
hence thesis by A35,Def1;
end;
hence thesis;
suppose A38:0. <' y & x=+infty & x * y = +infty;
now per cases by SUPINF_1:22;
suppose A39:0. <' z;
then A40: x * y * z = +infty by A38,Def1;
0. <' y * z by A38,A39,Th20;
hence thesis by A38,A40,Def1;
suppose A41:0. = z;
then A42: x * y * z = 0. by Def1;
y * z = 0. by A41,Def1;
hence thesis by A42,Def1;
suppose A43:z <' 0.;
then A44: x * y * z = -infty by A38,Def1;
y * z <' 0. by A38,A43,Th21;
hence thesis by A38,A44,Def1;
end;
hence thesis;
suppose A45:x <' 0. & y = -infty & x * y = +infty;
now per cases by SUPINF_1:22;
suppose A46:0. <' z;
then x * y * z = +infty by A45,Def1;
hence thesis by A45,A46,Def1;
suppose A47:0. = z;
then A48: x * y * z = 0. by Def1;
y * z = 0. by A47,Def1;
hence thesis by A48,Def1;
suppose A49:z <' 0.;
then A50: x * y * z = -infty by A45,Def1;
y * z = +infty by A45,A49,Def1;
hence thesis by A45,A50,Def1;
end;
hence thesis;
suppose A51:y <' 0. & x = -infty & x * y = +infty;
now per cases by SUPINF_1:22;
suppose A52:0. <' z;
then A53: x * y * z = +infty by A51,Def1;
y * z <' 0. by A51,A52,Th21;
hence thesis by A51,A53,Def1;
suppose A54:0. = z;
then A55: x * y * z = 0. by Def1;
y * z = 0. by A54,Def1;
hence thesis by A55,Def1;
suppose A56:z <' 0.;
then A57: x * y * z = -infty by A51,Def1;
0. <' y * z by A51,A56,Th20;
hence thesis by A51,A57,Def1;
end;
hence thesis;
suppose A58:x <' 0. & y=+infty & x * y = -infty;
now per cases by SUPINF_1:22;
suppose A59:0. <' z;
then y * z = +infty by A58,Def1;
hence thesis by A58,A59,Def1;
suppose A60:0. = z;
then A61: x * y * z = 0. by Def1;
y * z = 0. by A60,Def1;
hence thesis by A61,Def1;
suppose A62:z <' 0.;
then A63: x * y * z = +infty by A58,Def1;
y * z = -infty by A58,A62,Def1;
hence thesis by A58,A63,Def1;
end;
hence thesis;
suppose A64:y <' 0. & x=+infty & x * y = -infty;
now per cases by SUPINF_1:22;
suppose A65:0. <' z;
then A66: x * y * z = -infty by A64,Def1;
y * z <' 0. by A64,A65,Th21;
hence thesis by A64,A66,Def1;
suppose A67:0. = z;
then A68: x * y * z = 0. by Def1;
y * z = 0. by A67,Def1;
hence thesis by A68,Def1;
suppose A69:z <' 0.;
then A70: x * y * z = +infty by A64,Def1;
0. <' y * z by A64,A69,Th20;
hence thesis by A64,A70,Def1;
end;
hence thesis;
suppose A71:0. <' x & y = -infty & x * y = -infty;
now per cases by SUPINF_1:22;
suppose 0. <' z;
then y * z = -infty by A71,Def1;
hence thesis by A71;
suppose A72:0. = z;
then A73: x * y * z = 0. by Def1;
y * z = 0. by A72,Def1;
hence thesis by A73,Def1;
suppose z <' 0.;
then y * z = +infty by A71,Def1;
hence thesis by A71,Def1;
end;
hence thesis;
suppose A74:0. <' y & x = -infty & x * y = -infty;
now per cases by SUPINF_1:22;
suppose A75:0. <' z;
then A76: x * y * z = -infty by A74,Def1;
0. <' y * z by A74,A75,Th20;
hence thesis by A74,A76,Def1;
suppose A77:0. = z;
then A78: x * y * z = 0. by Def1;
y * z = 0. by A77,Def1;
hence thesis by A78,Def1;
suppose A79:z <' 0.;
then A80: x * y * z = +infty by A74,Def1;
y * z <' 0. by A74,A79,Th21;
hence thesis by A74,A80,Def1;
end;
hence thesis;
suppose A81:x = 0. & x * y = 0.;
then x * y * z = 0. by Def1;
hence thesis by A81,Def1;
suppose A82:y = 0. & x * y = 0.;
then x * y * z = 0. by Def1;
hence thesis by A82;
end;
hence thesis;
end;

theorem Th24:
-0. = 0. by REAL_1:26,SUPINF_2:3,def 1;

theorem
(0. <' x iff -x <' 0.) & (x <' 0. iff 0. <' -x) by Th24,SUPINF_2:17;

theorem Th26:
-(x * y) = x * (-y) & -(x * y) = (-x) * y
proof
now per cases by Def1;
suppose ex a,b being Real st (x = a & y = b & x * y = a * b);
then consider a,b being Real such that
A1: x = a & y = b & x * y = a * b;
A2: -x = -a & -y = -b & -(x * y) = -(a * b) by A1,SUPINF_2:3;
then x * (-y) = a * (-b) & (-x) * y = (-a) * b by A1,Th13;
hence thesis by A2,XCMPLX_1:175;
suppose A3:((0. <' x & y=+infty) or (0. <' y & x=+infty) or
(x <' 0. & y=-infty) or (y <' 0. & x = -infty)) & x * y = +infty;
then A4: -(x * y) = -infty by Th4;
A5: ((-x <' 0. & y=+infty) or (0. <' y & -x=-infty) or
(0.<'-x & y=-infty) or (y<'0. & -x=+infty))
by A3,Th4,Th24,SUPINF_2:17;
((0. <' x & -y=-infty) or (-y <' 0. & x=+infty) or
(x<'0. & -y=+infty) or (0.<'-y & x=-infty))
by A3,Th4,Th24,SUPINF_2:17;
hence thesis by A4,A5,Def1;
suppose A6:((x <' 0. & y=+infty) or (y <' 0. & x=+infty) or
(0. <' x & y=-infty) or (0. <' y & x = -infty)) & x * y = -infty;
then A7: -(x * y) = +infty by Th4;
A8: ((0. <' -x & y=+infty) or (y <' 0. & -x=-infty) or
(-x <' 0. & y=-infty) or (0. <' y & -x=+infty))
by A6,Th4,Th24,SUPINF_2:17;
((x <' 0. & -y=-infty) or (0. <' -y & x=+infty) or
(0. <' x & -y=+infty) or (-y <' 0. & x=-infty))
by A6,Th4,Th24,SUPINF_2:17;
hence thesis by A7,A8,Def1;
suppose (x = 0. or y = 0.) & x * y = 0.;
hence thesis by Def1,Th24;
end;
hence thesis;
end;

theorem
x <> +infty & x <> -infty & x * y = +infty implies y = +infty or y = -infty
proof
assume A1:x <> +infty & x <> -infty & x * y = +infty;
assume A2:y <> +infty & y <> -infty;
reconsider a=x as Real by A1,Th1;
reconsider b=y as Real by A2,Th1;
x * y = a * b by Th13;
end;

theorem
x <> +infty & x <> -infty & x * y = -infty implies y = +infty or y = -infty
proof
assume A1:x <> +infty & x <> -infty & x * y = -infty;
assume A2:y <> +infty & y <> -infty;
reconsider a=x as Real by A1,Th1;
reconsider b=y as Real by A2,Th1;
x * y = a * b by Th13;
end;

theorem Th29:
x <> +infty & x <> -infty implies x * (y + z) = x * y + x * z
proof
assume
x <> +infty & x <> -infty;
then reconsider a = x as Real by Th1;
per cases by SUPINF_2:def 2;
suppose A1: y + z = 0.;
y = -z
proof
assume A2: y <> -z;
then A3:   -y <> z;
per cases by SUPINF_2:2;
suppose A4: y in REAL;
z in REAL
proof
assume A5: not z in REAL;
per cases by A5,SUPINF_2:2;
suppose z = -infty;
hence thesis by A1,A4,Lm1,SUPINF_2:19;
suppose z = +infty;
hence thesis by A1,A4,Lm1,SUPINF_2:19;
end;
then consider a,b being Real such that
A6:    y = a & z = b & y + z = a + b by A4,SUPINF_2:def 2;
consider a' being Real such that
A7:   y = a' & -y = -a' by A4,SUPINF_2:def 3;
z <> -a by A2,A6,A7;
hence thesis by A1,A6,SUPINF_2:def 1,XCMPLX_0:def 6;
suppose y = -infty;
hence thesis by A1,A3,SUPINF_2:4,19,def 2;

suppose A8: y = +infty;
then z <> -infty by A3,SUPINF_2:def 3;
hence thesis by A1,A8,SUPINF_2:19,def 2;
end;
then x * y + x * z = -(x * z) + x * z by Th26
.= 0. by Th9;
hence thesis by A1,Def1;
suppose y in REAL & z in REAL;
then consider b,c being Real such that
A9: y = b & z = c & y + z = b + c by SUPINF_2:def 2;
A10: x * (y + z) = a * (b + c) by A9,Th13 .= a * b + a * c by XCMPLX_1:8;
x * y = a * b & x * z = a * c by A9,Th13;
hence thesis by A10,SUPINF_2:1;
suppose A11:y = +infty & z <> -infty;
now per cases;
suppose a < 0;
then A12:  x <' 0. by Lm4;
then A13:  x * y = -infty by A11,Def1;
now per cases;
suppose z = +infty;
then x * z = -infty by A12,Def1;
then x * y + x * z = -infty by A13,SUPINF_1:14,SUPINF_2:def 2;
hence thesis by A11,A13,SUPINF_2:def 2;
suppose z <> +infty;
then reconsider c = z as Real by A11,Th1;
x * z = a * c by Th13;
then A14:    +infty <> x * z by SUPINF_1:31;
y + z = +infty by A11,SUPINF_2:def 2;
then x * (y + z) = -infty by A12,Def1;
hence thesis by A13,A14,SUPINF_2:def 2;
end;
hence thesis;
suppose a = 0;
then x * (y + z) = 0. & x * y = 0. & x * z = 0. by Def1,SUPINF_2:def 1;
hence thesis by SUPINF_2:18;
suppose a > 0;
then A15:  0. <' x by Lm3;
then A16:  x * y = +infty by A11,Def1;
now per cases;
suppose z = +infty;
then x * z = +infty by A15,Def1;
then x * y + x * z = +infty by A16,SUPINF_1:14,SUPINF_2:def 2;
hence thesis by A11,A16,SUPINF_2:def 2;
suppose z <> +infty;
then reconsider c = z as Real by A11,Th1;
x * z = a * c by Th13;
then A17:    -infty <> x * z by SUPINF_1:31;
y + z = +infty by A11,SUPINF_2:def 2;
then x * (y + z) = +infty by A15,Def1;
hence thesis by A16,A17,SUPINF_2:def 2;
end;
hence thesis;
end;
hence thesis;

suppose A18:y = -infty & z <> +infty;
now per cases;
suppose a < 0;
then A19:  x <' 0. by Lm4;
then A20:  x * y = +infty by A18,Def1;
now per cases;
suppose z = -infty;
then x * z = +infty by A19,Def1;
then x * y + x * z = +infty by A20,SUPINF_1:14,SUPINF_2:def 2;
hence thesis by A18,A20,SUPINF_2:def 2;
suppose z <> -infty;
then reconsider c = z as Real by A18,Th1;
x * z = a * c by Th13;
then A21:    -infty <> x * z by SUPINF_1:31;
y + z = -infty by A18,SUPINF_2:def 2;
then x * (y + z) = +infty by A19,Def1;
hence thesis by A20,A21,SUPINF_2:def 2;
end;
hence thesis;
suppose a = 0;
then x * (y + z) = 0. & x * y = 0. & x * z = 0. by Def1,SUPINF_2:def 1;
hence thesis by SUPINF_2:18;
suppose a > 0;
then A22: 0. <' x by Lm3;
then A23: x * y = -infty by A18,Def1;
now per cases;
suppose z = -infty;
then x * z = -infty by A22,Def1;
then x * y + x * z = -infty by A23,SUPINF_1:14,SUPINF_2:def 2;
hence thesis by A18,A23,SUPINF_2:def 2;
suppose z <> -infty;
then reconsider c = z as Real by A18,Th1;
x * z = a * c by Th13;
then A24:    +infty <> x * z by SUPINF_1:31;
y + z = -infty by A18,SUPINF_2:def 2;
then x * (y + z) = -infty by A22,Def1;
hence thesis by A23,A24,SUPINF_2:def 2;
end;
hence thesis;
end;
hence thesis;

suppose A25:z = +infty & y <> -infty;
now per cases;
suppose a < 0;
then A26:  x <' 0. by Lm4;
then A27:  x * z = -infty by A25,Def1;
now per cases;
suppose y = +infty;
then x * y = -infty by A26,Def1;
then x * y + x * z = -infty by A27,SUPINF_1:14,SUPINF_2:def 2;
hence thesis by A25,A27,SUPINF_2:def 2;

suppose y <> +infty;
then reconsider b = y as Real by A25,Th1;
A28:    x * y = a * b by Th13;
y + z = +infty by A25,SUPINF_2:def 2;
then x * (y + z) = -infty by A26,Def1;
hence thesis by A27,A28,Lm1;
end;
hence thesis;
suppose a = 0;
then x * (y + z) = 0. & x * y = 0. & x * z = 0. by Def1,SUPINF_2:def 1;
hence thesis by SUPINF_2:18;
suppose a > 0;
then A29: 0. <' x by Lm3;
then A30: x * z = +infty by A25,Def1;
now per cases;
suppose y = +infty;
then x * y = +infty by A29,Def1;
then x * y + x * z = +infty by A30,SUPINF_1:14,SUPINF_2:def 2;
hence thesis by A25,A30,SUPINF_2:def 2;

suppose y <> +infty;
then reconsider b = y as Real by A25,Th1;
A31:    x * y = a * b by Th13;
y + z = +infty by A25,SUPINF_2:def 2;
then x * (y + z) = +infty by A29,Def1;
hence thesis by A30,A31,Lm1;
end;
hence thesis;
end;
hence thesis;

suppose A32:z = -infty & y <> +infty;
now per cases;
suppose a < 0;
then A33:  x <' 0. by Lm4;
then A34:  x * z = +infty by A32,Def1;
now per cases;
suppose y = -infty;
then x * y = +infty by A33,Def1;
then x * y + x * z = +infty by A34,SUPINF_1:14,SUPINF_2:def 2;
hence thesis by A32,A34,SUPINF_2:def 2;

suppose y <> -infty;
then reconsider b = y as Real by A32,Th1;
A35:    x * y = a * b by Th13;
y + z = -infty by A32,SUPINF_2:def 2;
then x * (y + z) = +infty by A33,Def1;
hence thesis by A34,A35,Lm1;
end;
hence thesis;
suppose a = 0;
then x * (y + z) = 0. & x * y = 0. & x * z = 0. by Def1,SUPINF_2:def 1;
hence thesis by SUPINF_2:18;
suppose a > 0;
then A36: 0. <' x by Lm3;
then A37: x * z = -infty by A32,Def1;
now per cases;
suppose y = -infty;
then x * y = -infty by A36,Def1;
then x * y + x * z = -infty by A37,SUPINF_1:14,SUPINF_2:def 2;
hence thesis by A32,A37,SUPINF_2:def 2;

suppose y <> -infty;
then reconsider b = y as Real by A32,Th1;
A38:    x * y = a * b by Th13;
y + z = -infty by A32,SUPINF_2:def 2;
then x * (y + z) = -infty by A36,Def1;
hence thesis by A37,A38,Lm1;
end;
hence thesis;
end;
hence thesis;
end;

theorem
not ((y = +infty & z = +infty) or (y = -infty & z = -infty)) &
x <> +infty & x <> -infty implies x * (y - z) = x * y - x * z
proof
assume not ((y = +infty & z = +infty) or (y = -infty & z = -infty)) &
x <> +infty & x <> -infty;
then A1:x * (y + -z) = x * y + x * (-z) by Th29;
y - (--z) = y + -z by Th5;
then x * (y - z) = x * y + -(x * z) by A1,Th26;
hence thesis by SUPINF_2:def 4;
end;

definition
let x,y be R_eal;
assume A1:not((x=-infty or x=+infty) & (y=-infty or y=+infty)) & y <> 0.;
func x / y -> R_eal means :Def2:
(ex a,b being Real st (x = a & y = b & it = a / b)) or
(((x=+infty & 0. <' y) or (x=-infty & y <' 0.)) & it = +infty) or
(((x=-infty & 0. <' y) or (x=+infty & y <' 0.)) & it = -infty) or
((y = -infty or y = +infty) & it = 0.);
existence
proof
now per cases by A1;
suppose x<>-infty & x<>+infty & y <> 0.;
then A2: x is Real by MEASURE3:2;
y in REAL or y in {-infty,+infty} by SUPINF_1:def 6,XBOOLE_0:def 2;
then A3: y in REAL or y = +infty or y = -infty by TARSKI:def 2;
ex Z being R_eal st
(ex a,b being Real st (x = a & y = b & Z = a / b)) or
((y = -infty or y = +infty) & Z = 0.)
proof
y in REAL implies ex Z being R_eal st
ex a,b being Real st (x = a & y = b & Z = a / b)
proof
assume y in REAL;
then consider a,b being Real such that
A4:   x = a & y = b by A2;
reconsider Z = a / b as R_eal by SUPINF_1:10;
take Z;
thus thesis by A4;
end;
hence thesis by A3;
end;
hence thesis;
suppose A5:y<>-infty & y<>+infty & y <> 0.;
then A6:y is Real by MEASURE3:2;
x in REAL or x in {-infty,+infty} by SUPINF_1:def 6,XBOOLE_0:def 2;
then A7:x in REAL or x = +infty or x = -infty by TARSKI:def 2;
ex Z being R_eal st
(ex a,b being Real st (x = a & y = b & Z = a / b)) or
(((x=+infty & 0. <' y) or (x=-infty & y <' 0.)) & Z = +infty) or
(((x=-infty & 0. <' y) or (x=+infty & y <' 0.)) & Z = -infty)
proof
A8: x in REAL implies ex Z being R_eal st
ex a,b being Real st x = a & y = b & Z = a / b
proof
assume x in REAL;
then consider a,b being Real such that
A9: x = a & y = b by A6;
reconsider Z = a / b as R_eal by SUPINF_1:10;
take Z;
thus thesis by A9;
end;
0. <' y or y <' 0. by A5,SUPINF_1:22;
hence thesis by A7,A8;
end;
hence thesis;
end;
hence thesis;
end;
uniqueness by A1,SUPINF_1:31;
end;

canceled;

theorem Th32: for x,y being R_eal st y <> 0. holds
for a,b being Real st x = a & y = b holds x / y = a / b
proof
let x,y be R_eal;
assume A1:y <> 0.;
let a,b be Real;
assume A2:x = a & y = b;
a <> +infty & a <> -infty & b <> +infty & b <> -infty by SUPINF_1:31;
then consider a1,b1 being Real such that
A3:x = a1 & y = b1 & x / y = a1 / b1 by A1,A2,Def2;
thus thesis by A2,A3;
end;

theorem for x,y being R_eal st x <> -infty & x <> +infty &
(y = -infty or y = +infty) holds x / y = 0. by Def2,SUPINF_2:19;

theorem for x being R_eal st x <> -infty & x <> +infty & x <> 0. holds
x / x = 1
proof
let x be R_eal;
assume A1:x <> -infty & x <> +infty & x <> 0.;
then consider a,b being Real such that
A2:x = a & x = b & x / x = a / b by Def2;
thus thesis by A1,A2,SUPINF_2:def 1,XCMPLX_1:60;
end;

definition let x be R_eal;
func |. x .| -> R_eal equals :Def3:
x if 0. <=' x otherwise -x;
coherence;
consistency;
end;

canceled;

theorem
for x being R_eal st 0. <' x holds |.x.| = x by Def3;

theorem
for x being R_eal st x <' 0. holds |.x.| = -x by Def3;

theorem
for a,b being Real holds R_EAL(a*b) = R_EAL a * R_EAL b
proof
let a,b be Real;
reconsider c = a*b as real number;
A1:R_EAL(a*b) = c by MEASURE6:def 1;
reconsider a,b as real number;
R_EAL a = a & R_EAL b = b by MEASURE6:def 1;
hence thesis by A1,Th13;
end;

theorem
for a,b being Real st b <> 0 holds R_EAL(a/b) = R_EAL a / R_EAL b
proof
let a,b be Real;
assume A1:b <> 0;
reconsider a,b as R_eal by SUPINF_1:10;
reconsider a,b as real number;
set c = a/b;
reconsider a,b as Real;
A2:R_EAL(a/b) = c by MEASURE6:def 1;
R_EAL a = a & R_EAL b = b by MEASURE6:def 1;
hence thesis by A1,A2,Th32,SUPINF_2:def 1;
end;

theorem
for x,y being R_eal st x <=' y & (x <' +infty & -infty <' y) holds 0. <=' y-x
proof
let x,y being R_eal;
assume that A1:x <=' y and A2:(x <' +infty & -infty <' y);
per cases;
suppose x = -infty;
hence thesis by A2,SUPINF_2:7,19;
suppose x <> -infty;
hence thesis by A1,A2,MEASURE5:1;
end;

theorem
for x,y being R_eal st x <' y & (x <' +infty & -infty <' y) holds 0. <' y-x
proof
let x,y be R_eal;
assume that A1:x <' y and A2:x <' +infty & -infty <' y;
per cases;
suppose y = +infty;
hence thesis by A2,SUPINF_2:6,19;
suppose A3:y <> +infty;
now per cases;
suppose x = -infty;
hence thesis by A2,SUPINF_2:7,19;
suppose A4:x <> -infty;
A5: y <=' +infty by SUPINF_1:20;
then A6:  x is Real by A1,A4,Th1;
reconsider a = x as Real by A1,A4,A5,Th1;
A7:  y is Real by A2,A3,Th1;
reconsider b = y as Real by A2,A3,Th1;
A8:  y - x = b - a by SUPINF_2:5;
consider p,q being Real such that
A9:  p = x & q = y & p <= q by A1,A6,A7,SUPINF_1:16;
a < b by A1,A9,REAL_1:def 5;
then b - a > 0 by SQUARE_1:11;
hence thesis by A8,Lm3;
end;
hence thesis;
end;

theorem
x <=' y & 0. <=' z implies x*z <=' y*z
proof
assume that A1:x <=' y and A2:0. <=' z;
per cases by A2,SUPINF_1:22;
suppose z = 0.;
then x*z = 0. & y*z = 0. by Def1;
hence thesis;
suppose A3:0. <' z;
now per cases;
suppose A4:x<' +infty & -infty <' y;
now per cases;
suppose A5:z = +infty;
now per cases by SUPINF_1:22;
suppose A6:x = 0.;
then A7:    x*z = 0. & 0. <=' y by A1,Def1;
now per cases by A1,A6,SUPINF_1:22;
suppose 0.= y;
hence thesis by A6;
suppose 0. <' y;
hence thesis by A3,A7,Th20;
end;
hence thesis;
suppose x <' 0.;
then x*z = -infty by A5,Def1;
hence thesis by SUPINF_1:21;
suppose A8:0. <' x;
then A9:    x*z = +infty by A5,Def1;
now per cases by A1,SUPINF_1:22;
suppose y = x;
hence thesis;
suppose x <' y;
then 0. <' y by A8,SUPINF_1:29; hence thesis by A5,A9,Def1;
end;
hence thesis;
end;
hence thesis;
suppose z <>+infty;
then reconsider c = z as Real by A3,Th1,SUPINF_2:19;
now per cases;
suppose x = -infty;
then x*z = -infty by A3,Def1;
hence thesis by SUPINF_1:21;
suppose x <> -infty;
then A10:   x is Real by A4,Th1;
now per cases;
suppose y = +infty;
then y*z = +infty by A3,Def1;
hence thesis by SUPINF_1:20;
suppose y <> +infty;
then y is Real by A4,Th1;
then consider a,b being Real such that
A11:    a = x & b = y & a <= b by A1,A10,SUPINF_1:16;
A12:    x*z = a*c & y*z = b*c by A11,Th13;
c > 0 by A3,SUPINF_1:16,SUPINF_2:def 1;
then a*c <= b*c by A11,AXIOMS:25;
hence thesis by A12,SUPINF_1:16;
end;
hence thesis;
end;
hence thesis;
end;
hence thesis;
suppose A13: not (x <' +infty & -infty <' y);
now per cases by A13,SUPINF_1:23,24;
suppose x = +infty; hence thesis by A1,SUPINF_1:24;
suppose y = -infty; hence thesis by A1,SUPINF_1:23;
end;
hence thesis;
end;
hence thesis;
end;

theorem
x <=' y & z <=' 0. implies y*z <=' x*z
proof
assume that A1:x <=' y and A2:z <=' 0.;
per cases by A2,SUPINF_1:22;
suppose z = 0.;
then x*z = 0. & y*z = 0. by Def1;
hence thesis;
suppose A3:z <' 0.;
now per cases;
suppose A4:x<' +infty & -infty <' y;
now per cases;
suppose A5:z = -infty;
now per cases by SUPINF_1:22;
suppose A6:x = 0.;
then A7:    x*z = 0. & 0. <=' y by A1,Def1;
now per cases by A1,A6,SUPINF_1:22;
suppose 0.= y;
hence thesis by A6;
suppose 0. <' y;
hence thesis by A3,A7,Th21;
end;
hence thesis;
suppose x <' 0.;
then x*z = +infty by A5,Def1;
hence thesis by SUPINF_1:20;
suppose A8:0. <' x;
then A9:    x*z = -infty by A5,Def1;
now per cases by A1,SUPINF_1:22;
suppose y = x;
hence thesis;
suppose x <' y;
then 0. <' y by A8,SUPINF_1:29; hence thesis by A5,A9,Def1;
end;
hence thesis;
end;
hence thesis;
suppose z <>-infty;
then reconsider c = z as Real by A3,Th1,SUPINF_2:19;
now per cases;
suppose x = -infty;
then x*z = +infty by A3,Def1;
hence thesis by SUPINF_1:20;
suppose x <> -infty;
then A10:   x is Real by A4,Th1;
now per cases;
suppose y = +infty;
then y*z = -infty by A3,Def1;
hence thesis by SUPINF_1:21;
suppose y <> +infty;
then y is Real by A4,Th1;
then consider a,b being Real such that
A11:    a = x & b = y & a <= b by A1,A10,SUPINF_1:16;
A12:    x*z = a*c & y*z = b*c by A11,Th13;
c < 0 by A3,SUPINF_1:16,SUPINF_2:def 1;
then a*c >= b*c by A11,REAL_1:52;
hence thesis by A12,SUPINF_1:16;
end;
hence thesis;
end;
hence thesis;
end;
hence thesis;
suppose A13: not (x <' +infty & -infty <' y);
now per cases by A13,SUPINF_1:23,24;
suppose x = +infty; hence thesis by A1,SUPINF_1:24;
suppose y = -infty; hence thesis by A1,SUPINF_1:23;
end;
hence thesis;
end;
hence thesis;
end;

theorem
x <' y & 0. <' z & z <> +infty implies x*z <' y*z
proof
assume that A1:x <' y and A2:0. <' z and A3:z <> +infty;
A4:x <' +infty & -infty <' y
proof
assume A5: not (x <' +infty & -infty <' y);
now per cases by A5,SUPINF_1:23,24;
suppose x = +infty;
suppose y = -infty;
end;
hence thesis;
end;
reconsider c = z as Real by A2,A3,Th1,SUPINF_2:19;
now per cases;
suppose x = -infty;
then A6:  x*z = -infty by A2,Def1;
now per cases;
suppose y = +infty;
then y * z = +infty by A2,Def1;
hence thesis by A6,SUPINF_1:29,SUPINF_2:19;
suppose y <> +infty;
then reconsider b = y as Real by A4,Th1;
y * z = b * c by Th13;
hence thesis by A6,SUPINF_1:31;
end;
hence thesis;
suppose A7:x <> -infty;
then A8: x is Real by A4,Th1;
reconsider a = x as Real by A4,A7,Th1;
A9:  x * z = a * c by Th13;
now per cases;
suppose y = +infty;
then y*z = +infty by A2,Def1;
hence thesis by A9,SUPINF_1:31;
suppose y <> +infty;
then y is Real by A4,Th1;
then consider a,b being Real such that
A10:  a = x & b = y & a <= b by A1,A8,SUPINF_1:16;
A11:   a < b by A1,A10,REAL_1:def 5;
A12:  x*z = a*c & y*z = b*c by A10,Th13;
c > 0 by A2,SUPINF_1:16,SUPINF_2:def 1;
then A13:   a*c <= b*c & a*c <> b*c by A11,REAL_1:70;
then x*z <=' y*z by A12,SUPINF_1:16;
hence thesis by A12,A13,SUPINF_1:22;
end;
hence thesis;
end;
hence thesis;
end;

theorem
x <' y & z <' 0. & z <> -infty implies y*z <' x*z
proof
assume that A1:x <' y and A2:z <' 0. and A3:z <> -infty;
A4:x <' +infty & -infty <' y
proof
assume A5: not (x <' +infty & -infty <' y);
now per cases by A5,SUPINF_1:23,24;
suppose x = +infty;
suppose y = -infty;
end;
hence thesis;
end;
reconsider c = z as Real by A2,A3,Th1,SUPINF_2:19;
now per cases;
suppose x = -infty;
then A6:  x*z = +infty by A2,Def1;
now per cases;
suppose y = +infty;
then y * z = -infty by A2,Def1;
hence thesis by A6,SUPINF_1:29,SUPINF_2:19;
suppose y <> +infty;
then reconsider b = y as Real by A4,Th1;
y * z = b * c by Th13;
hence thesis by A6,SUPINF_1:31;
end;
hence thesis;
suppose A7:x <> -infty;
then A8: x is Real by A4,Th1;
reconsider a = x as Real by A4,A7,Th1;
A9:  x * z = a * c by Th13;
now per cases;
suppose y = +infty;
then y*z = -infty by A2,Def1;
hence thesis by A9,SUPINF_1:31;
suppose y <> +infty;
then y is Real by A4,Th1;
then consider a,b being Real such that
A10:  a = x & b = y & a <= b by A1,A8,SUPINF_1:16;
A11:   a < b by A1,A10,REAL_1:def 5;
A12:  x*z = a*c & y*z = b*c by A10,Th13;
c < 0 by A2,SUPINF_1:16,SUPINF_2:def 1;
then A13:   a*c >= b*c & a*c <> b*c by A11,REAL_1:71;
then y*z <=' x*z by A12,SUPINF_1:16;
hence thesis by A12,A13,SUPINF_1:22;
end;
hence thesis;
end;
hence thesis;
end;

theorem
(x is Real & y is Real) implies
(x <' y iff ex p,q being Real st (p = x & q = y & p < q))
proof
assume A1:x is Real & y is Real;
then reconsider a = x as Real;
reconsider b = y as Real by A1;
x <' y implies ex p,q being Real st (p = x & q = y & p < q)
proof
assume x <' y;
then a < b by HAHNBAN:12;
hence thesis;
end;
hence thesis by HAHNBAN:12;
end;

theorem
x <> -infty & y <> +infty & x <=' y & 0. <' z implies x/z <=' y/z
proof
assume that A1:x <> -infty & y <> +infty and A2:x <=' y and
A3:0. <' z;
A4:x <> +infty & y <> -infty by A1,A2,Th7;
then reconsider a = x as Real by A1,Th1;
reconsider b = y as Real by A1,A4,Th1;
now per cases;
suppose A5:z = +infty;
then x/z = 0. by A1,A3,A4,Def2;
hence thesis by A1,A3,A4,A5,Def2;
suppose A6: z <> +infty;
then z <> -infty by A3,Th7;
then reconsider c = z as Real by A6,Th1;
A7: x/z = a/c & y/z = b/c by A3,Th32;
a <= b & 0 < c by A2,A3,HAHNBAN:12,SUPINF_2:def 1;
then a/c <= b/c by REAL_1:73;
hence thesis by A7,HAHNBAN:12;
end;
hence thesis;
end;

theorem
x <=' y & 0. <' z & z <> +infty implies x/z <=' y/z
proof
assume that A1:x <=' y and A2:0. <' z and A3:z <> +infty;
A4:z <> -infty by A2,A3,Th7;
now per cases;
suppose A5:x<>-infty;
now per cases;
suppose A6:y <> +infty;
-infty <=' x & y <=' +infty by SUPINF_1:20,21;
then A7: -infty <' x & y <' +infty by A5,A6,SUPINF_1:22;
then reconsider a = x as Real by A1,Th1;
reconsider b = y as Real by A1,A7,Th1;
z <> -infty by A2,A3,Th7;
then reconsider c = z as Real by A3,Th1;
A8:  x/z = a/c & y/z = b/c by A2,Th32;
a <= b & 0 < c by A1,A2,HAHNBAN:12,SUPINF_2:def 1;
then a/c <= b/c by REAL_1:73;
hence thesis by A8,HAHNBAN:12;
suppose y = +infty;
then y/z = +infty by A2,A3,A4,Def2;
hence thesis by SUPINF_1:20;
end;
hence thesis;
suppose x=-infty;
then x/z = -infty by A2,A3,A4,Def2;
hence thesis by SUPINF_1:21;
end;
hence thesis;
end;

theorem
x <> -infty & y <> +infty & x <=' y & z <' 0. implies y/z <=' x/z
proof
assume that A1:x <> -infty & y <> +infty and A2:x <=' y and
A3:z <' 0.;
A4:x <> +infty & y <> -infty by A1,A2,Th7;
then reconsider a = x as Real by A1,Th1;
reconsider b = y as Real by A1,A4,Th1;
now per cases;
suppose A5:z = -infty;
then x/z = 0. by A1,A3,A4,Def2;
hence thesis by A1,A3,A4,A5,Def2;
suppose z <> -infty;
then reconsider c = z as Real by A3,Th1,SUPINF_2:19;
A6: x/z = a/c & y/z = b/c by A3,Th32;
a <= b & 0 > c by A2,A3,HAHNBAN:12,SUPINF_2:def 1;
then a/c >= b/c by REAL_1:74;
hence thesis by A6,HAHNBAN:12;
end;
hence thesis;
end;

theorem
x <=' y & z <' 0. & z <> -infty implies y/z <=' x/z
proof
assume that A1:x <=' y and A2:z <' 0. and A3:z <> -infty;
A4:z <> +infty by A2,A3,Th7;
now per cases;
suppose A5:x<>-infty;
now per cases;
suppose A6:y <> +infty;
-infty <=' x & y <=' +infty by SUPINF_1:20,21;
then A7: -infty <' x & y <' +infty by A5,A6,SUPINF_1:22;
then reconsider a = x as Real by A1,Th1;
reconsider b = y as Real by A1,A7,Th1;
reconsider c = z as Real by A2,A3,Th1,SUPINF_2:19;
A8:  x/z = a/c & y/z = b/c by A2,Th32;
a <= b & c < 0 by A1,A2,HAHNBAN:12,SUPINF_2:def 1;
then a/c >= b/c by REAL_1:74;
hence thesis by A8,HAHNBAN:12;
suppose y = +infty;
then y/z = -infty by A2,A3,A4,Def2;
hence thesis by SUPINF_1:21;
end;
hence thesis;
suppose x=-infty;
then x/z = +infty by A2,A3,A4,Def2;
hence thesis by SUPINF_1:20;
end;
hence thesis;
end;

theorem
x <' y & 0. <' z & z <> +infty implies x/z <' y/z
proof
assume that A1:x <' y and A2:0. <' z & z <> +infty;
A3:x <> +infty & y <> -infty by A1,Th3;
A4:z <> -infty by A2,Th7;
then reconsider c = z as Real by A2,Th1;
now per cases;
suppose y <> +infty;
then reconsider b = y as Real by A3,Th1;
A5: y/z = b/c by A2,Th32;
now per cases;
suppose x <> -infty;
then reconsider a = x as Real by A3,Th1;
A6:  x/z = a/c by A2,Th32;
a < b & 0 < c by A1,A2,HAHNBAN:12,SUPINF_2:def 1;
then a/c < b/c by REAL_1:73;
hence thesis by A5,A6,HAHNBAN:12;
suppose x = -infty;
then x/z = -infty by A2,A4,Def2;
hence thesis by A5,SUPINF_1:31;
end;
hence thesis;
suppose y = +infty;
then A7: y/z = +infty by A2,A4,Def2;
now per cases;
suppose x <> -infty;
then reconsider a = x as Real by A3,Th1;
x/z = a/c by A2,Th32;
hence thesis by A7,SUPINF_1:31;
suppose x = -infty;
hence thesis by A2,A4,A7,Def2,Th2;
end;
hence thesis;
end;
hence thesis;
end;

theorem
x <' y & z <' 0. & z <> -infty implies y/z <' x/z
proof
assume that A1:x <' y and A2:z <' 0. & z <> -infty;
A3:x <> +infty & y <> -infty by A1,Th3;
A4:z <> +infty by A2,Th7;
then reconsider c = z as Real by A2,Th1;
per cases;
suppose y <> +infty;
then reconsider b = y as Real by A3,Th1;
A5: y/z = b/c by A2,Th32;
now per cases;
suppose x <> -infty;
then reconsider a = x as Real by A3,Th1;
A6:  x/z = a/c by A2,Th32;
a < b & c < 0 by A1,A2,HAHNBAN:12,SUPINF_2:def 1;
then a/c > b/c by REAL_1:74;
hence thesis by A5,A6,HAHNBAN:12;
suppose x = -infty;
then x/z = +infty by A2,A4,Def2;
hence thesis by A5,SUPINF_1:31;
end;
hence thesis;
suppose y = +infty;
then A7: y/z = -infty by A2,A4,Def2;
now per cases;
suppose x <> -infty;
then reconsider a = x as Real by A3,Th1;
x/z = a/c by A2,Th32;
hence thesis by A7,SUPINF_1:31;
suppose x = -infty;
hence thesis by A2,A4,A7,Def2,Th2;
end;
hence thesis;
end;