:: Category of Rings
:: by Micha{\l} Muzalewski
::
:: Received December 5, 1991
:: Copyright (c) 1991-2018 Association of Mizar Users
:: (Stowarzyszenie Uzytkownikow Mizara, Bialystok, Poland).
:: This code can be distributed under the GNU General Public Licence
:: version 3.0 or later, or the Creative Commons Attribution-ShareAlike
:: License version 3.0 or later, subject to the binding interpretation
:: detailed in file COPYING.interpretation.
:: See COPYING.GPL and COPYING.CC-BY-SA for the full text of these
:: licenses, or see http://www.gnu.org/licenses/gpl.html and
:: http://creativecommons.org/licenses/by-sa/3.0/.
environ
vocabularies XBOOLE_0, CLASSES2, ALGSTR_0, FUNCT_1, FDIFF_1, MSSUBFAM,
GROUP_1, RELAT_1, VECTSP_1, ARYTM_3, MOD_2, FUNCSDOM, GRCAT_1, GRAPH_1,
STRUCT_0, MIDSP_1, XXREAL_0, CAT_1, SUBSET_1, ENS_1, SUPINF_2, MESFUNC1,
TARSKI, PARTFUN1, ZFMISC_1, RINGCAT1, MONOID_0, RELAT_2, BINOP_1;
notations TARSKI, XBOOLE_0, ZFMISC_1, XTUPLE_0, SUBSET_1, MCART_1, RELSET_1,
PARTFUN1, FUNCT_2, BINOP_1, STRUCT_0, ALGSTR_0, GROUP_1, VECTSP_1,
GRCAT_1, GRAPH_1, CAT_1, CLASSES2, MOD_2, GROUP_6;
constructors GRCAT_1, GROUP_6, MOD_2, RELSET_1, XTUPLE_0;
registrations XBOOLE_0, RELSET_1, FUNCT_2, STRUCT_0, GRCAT_1, MOD_2, VECTSP_1;
requirements SUBSET, BOOLE;
definitions GROUP_1, GROUP_6, VECTSP_1, CAT_1;
equalities GRCAT_1, STRUCT_0, GRAPH_1, CAT_1;
expansions GROUP_1, GROUP_6, VECTSP_1, CAT_1;
theorems CAT_1, FUNCT_2, GRCAT_1, MOD_2, TARSKI, RELAT_1, ZFMISC_1, XBOOLE_0,
FUNCT_1, BINOP_1, GROUP_6, SUBSET_1, VECTSP_1, XTUPLE_0;
schemes FUNCT_2, BINOP_1, TARSKI;
begin
reserve x,y for set;
reserve D for non empty set;
reserve UN for Universe;
::
:: 1a. Maps of the carriers of rings
::
definition
let G,H be non empty doubleLoopStr;
let IT be Function of G,H;
attr IT is linear means
IT is additive multiplicative unity-preserving;
end;
registration
let G,H be non empty doubleLoopStr;
cluster linear -> additive multiplicative unity-preserving
for Function of G,H;
coherence;
cluster additive multiplicative unity-preserving -> linear
for Function of G,H;
coherence;
end;
theorem Th1:
for G1,G2,G3 being non empty doubleLoopStr, f being Function of
G1,G2, g being Function of G2,G3 st f is linear & g is linear holds g*f is
linear
proof
let G1,G2,G3 be non empty doubleLoopStr, f be Function of G1,G2, g be
Function of G2,G3 such that
A1: f is additive multiplicative unity-preserving and
A2: g is additive multiplicative unity-preserving;
set h = g*f;
thus h is additive
proof
let x,y be Scalar of G1;
A3: g.(f.x) = h.x & g.(f.y) = h.y by FUNCT_2:15;
thus h.(x+y) = g.(f.(x+y)) by FUNCT_2:15
.= g.(f.x+f.y) by A1
.= h.x+h.y by A2,A3;
end;
thus h is multiplicative
proof
let x,y be Scalar of G1;
A4: g.(f.x) = h.x & g.(f.y) = h.y by FUNCT_2:15;
thus h.(x*y) = g.(f.(x*y)) by FUNCT_2:15
.= g.(f.x*f.y) by A1
.= h.x*h.y by A2,A4;
end;
thus h.(1_G1) = g.(f.(1_G1)) by FUNCT_2:15
.= g.(1_G2) by A1
.= 1_G3 by A2;
end;
::
:: 1b. Morphisms of rings
::
definition
struct RingMorphismStr (# Dom,Cod -> Ring, Fun -> Function of the Dom, the
Cod #);
end;
reserve f for RingMorphismStr;
definition
let f;
func dom(f) -> Ring equals
the Dom of f;
coherence;
func cod(f) -> Ring equals
the Cod of f;
coherence;
func fun(f) -> Function of the Dom of f, the Cod of f equals
the Fun of f;
coherence;
end;
reserve G,H,G1,G2,G3,G4 for Ring;
Lm1: for G being non empty doubleLoopStr holds id G is linear
proof
let G be non empty doubleLoopStr;
set f = id G;
thus f is additive;
thus f is multiplicative
proof
let x,y be Scalar of G;
f.(x*y) = x*y & f.x = x by FUNCT_1:18;
hence thesis by FUNCT_1:18;
end;
thus f.(1_G) = 1_G by FUNCT_1:18;
end;
registration
let G be non empty doubleLoopStr;
cluster id G -> linear;
coherence by Lm1;
end;
definition
let IT be RingMorphismStr;
attr IT is RingMorphism-like means
:Def5:
fun(IT) is linear;
end;
registration
cluster strict RingMorphism-like for RingMorphismStr;
existence
proof
set G = the Ring;
set i = RingMorphismStr(# G,G,id G#);
fun(i) = id G;
hence thesis by Def5;
end;
end;
definition
mode RingMorphism is RingMorphism-like RingMorphismStr;
end;
definition
let G;
func ID G -> RingMorphism equals
RingMorphismStr(# G,G,id G#);
coherence
proof
set i = RingMorphismStr(# G,G,id G#);
fun(i) = id G;
hence thesis by Def5;
end;
end;
registration
let G;
cluster ID G -> strict;
coherence;
end;
reserve F for RingMorphism;
definition
let G,H;
pred G <= H means
ex F being RingMorphism st dom(F) = G & cod(F) = H;
reflexivity
proof
let G;
set i = ID(G);
take i;
thus thesis;
end;
end;
Lm2: the RingMorphismStr of F is RingMorphism-like
proof
set S = the RingMorphismStr of F;
A1: fun F is linear by Def5;
hence for x,y being Scalar of the Dom of S holds (fun S).(x+y) = (fun S).x+(
fun S).y by VECTSP_1:def 20;
thus for x,y being Scalar of the Dom of S holds (fun S).(x*y) = (fun S).x*(
fun S).y by A1,GROUP_6:def 6;
thus thesis by A1;
end;
definition
let G,H;
assume
A1: G <= H;
mode Morphism of G,H -> strict RingMorphism means
:Def8:
dom(it) = G & cod( it) = H;
existence
proof
consider F being RingMorphism such that
A2: dom(F) = G & cod(F) = H by A1;
set S = the RingMorphismStr of F;
A3: dom S = G & cod S = H by A2;
S is RingMorphism by Lm2;
hence thesis by A3;
end;
end;
registration
let G,H;
cluster strict for Morphism of G,H;
existence
proof
set m = the Morphism of G,H;
m is RingMorphism;
hence thesis;
end;
end;
definition
let G;
redefine func ID G -> strict Morphism of G,G;
coherence
proof
set i = ID(G);
dom(i) = G & cod(i) = G;
hence thesis by Def8;
end;
end;
Lm3: the Fun of F is linear
proof
the Fun of F = fun(F);
hence thesis by Def5;
end;
Lm4: for f being strict RingMorphismStr holds dom(f) = G & cod(f) = H & fun(f)
is linear implies f is Morphism of G,H
proof
let f be strict RingMorphismStr;
assume that
A1: dom(f) = G and
A2: cod(f) = H and
A3: fun(f) is linear;
reconsider f9 = f as RingMorphism by A3,Def5;
dom(f9) = G by A1;
then G <= H by A2;
then f9 is Morphism of G,H by A1,A2,Def8;
hence thesis;
end;
Lm5: for f being Function of G,H st f is linear holds RingMorphismStr (#G,H,f
#) is Morphism of G,H
proof
let f be Function of G,H such that
A1: f is linear;
set F = RingMorphismStr (#G,H,f#);
A2: fun(F) = f;
dom(F) = G & cod(F) = H;
hence thesis by A1,A2,Lm4;
end;
Lm6: for F being RingMorphism ex G,H st G <= H & dom(F) = G & cod(F) = H & the
RingMorphismStr of F is Morphism of G,H
proof
let F be RingMorphism;
reconsider S = the RingMorphismStr of F as RingMorphism by Lm2;
set G = the Dom of F, H = the Cod of F;
take G,H;
dom(F) = G & cod(F) = H;
then
A1: G <= H;
dom S = G & cod S = H;
hence thesis by A1,Def8;
end;
theorem Th2:
for g,f being RingMorphism st dom(g) = cod(f) ex G1,G2,G3 st G1
<= G2 & G2 <= G3 & the RingMorphismStr of g is Morphism of G2,G3 & the
RingMorphismStr of f is Morphism of G1,G2
proof
defpred P[RingMorphism,RingMorphism] means dom($1) = cod($2);
let g,f be RingMorphism such that
A1: P[g,f];
( ex G2,G3 st G2 <= G3 & dom(g) = G2 & cod(g) = G3 & the RingMorphismStr
of g is Morphism of G2,G3)& ex G1,G29 being Ring st G1 <= G29 & dom(f) = G1 &
cod(f ) = G29 & the RingMorphismStr of f is Morphism of G1,G29 by Lm6;
hence thesis by A1;
end;
theorem Th3:
for F being strict RingMorphism holds F is Morphism of dom(F),cod
(F) & dom(F) <= cod(F)
proof
let F be strict RingMorphism;
ex G,H st G <= H & dom(F) = G & cod(F) = H & F is Morphism of G,H by Lm6;
hence thesis;
end;
Lm7: for F being Morphism of G,H st G <= H holds ex f being Function of G,H st
F = RingMorphismStr(#G,H,f#) & f is linear
proof
let F be Morphism of G,H such that
A1: G <= H;
A2: the Cod of F = cod(F) .= H by A1,Def8;
A3: the Dom of F = dom(F) .= G by A1,Def8;
then reconsider f = the Fun of F as Function of G,H by A2;
take f;
thus thesis by A3,A2,Lm3;
end;
Lm8: for F being Morphism of G,H st G <= H holds ex f being Function of G,H st
F = RingMorphismStr(#G,H,f#)
proof
let F be Morphism of G,H;
assume G <= H;
then consider f being Function of G,H such that
A1: F = RingMorphismStr(#G,H,f#) and
f is linear by Lm7;
take f;
thus thesis by A1;
end;
theorem
for F being strict RingMorphism ex G,H st ex f being Function of G,H
st F is Morphism of G,H & F = RingMorphismStr(#G,H,f#) & f is linear
proof
let F be strict RingMorphism;
consider G,H such that
A1: G <= H and
dom(F) = G and
cod(F) = H and
A2: F is Morphism of G,H by Lm6;
reconsider F9 = F as Morphism of G,H by A2;
consider f being Function of G,H such that
A3: F9 = RingMorphismStr(#G,H,f#) & f is linear by A1,Lm7;
take G,H,f;
thus thesis by A3;
end;
definition
let G,F be RingMorphism;
assume
A1: dom(G) = cod(F);
func G*F -> strict RingMorphism means
:Def9:
for G1,G2,G3 for g being
Function of G2,G3, f being Function of G1,G2 st the RingMorphismStr of G =
RingMorphismStr(#G2,G3,g#) & the RingMorphismStr of F = RingMorphismStr(#G1,G2,
f#) holds it = RingMorphismStr(#G1,G3,g*f#);
existence
proof
consider G19,G29,G39 being Ring such that
A2: G19 <= G29 and
A3: G29 <= G39 & the RingMorphismStr of G is Morphism of G29,G39 and
A4: the RingMorphismStr of F is Morphism of G19,G29 by A1,Th2;
consider g9 being Function of G29,G39 such that
A5: the RingMorphismStr of G = RingMorphismStr(#G29,G39,g9#) and
A6: g9 is linear by A3,Lm7;
consider f9 being Function of G19,G29 such that
A7: the RingMorphismStr of F = RingMorphismStr(#G19,G29,f9#) and
A8: f9 is linear by A2,A4,Lm7;
g9*f9 is linear by A6,A8,Th1;
then reconsider
T9 = (RingMorphismStr(#G19,G39,g9*f9#)) as strict RingMorphism
by Lm5;
take T9;
thus thesis by A5,A7;
end;
uniqueness
proof
consider G19,G299 being Ring such that
G19 <= G299 and
A9: dom(F) = G19 and
A10: cod(F) = G299 and
A11: the RingMorphismStr of F is Morphism of G19,G299 by Lm6;
reconsider F9 = the RingMorphismStr of F as Morphism of G19,G299 by A11;
let S1,S2 be strict RingMorphism such that
A12: for G1,G2,G3 for g being Function of G2,G3, f being Function of
G1,G2 st the RingMorphismStr of G = RingMorphismStr(#G2,G3,g#) & the
RingMorphismStr of F = RingMorphismStr(#G1,G2,f#) holds S1 = RingMorphismStr(#
G1,G3,g*f#) and
A13: for G1,G2,G3 for g being Function of G2,G3, f being Function of
G1,G2 st the RingMorphismStr of G = RingMorphismStr(#G2,G3,g#) & the
RingMorphismStr of F = RingMorphismStr(#G1,G2,f#) holds S2 = RingMorphismStr(#
G1,G3,g*f#);
consider G29,G39 being Ring such that
A14: G29 <= G39 and
A15: dom(G) = G29 and
cod(G) = G39 and
A16: the RingMorphismStr of G is Morphism of G29,G39 by Lm6;
reconsider F9 as Morphism of G19,G29 by A1,A15,A10;
consider f9 being Function of G19,G29 such that
A17: F9 = RingMorphismStr(#G19,G29,f9#) by A1,A15,A9;
reconsider G9 = the RingMorphismStr of G as Morphism of G29,G39 by A16;
consider g9 being Function of G29,G39 such that
A18: G9 = RingMorphismStr(#G29,G39,g9#) by A14,Lm8;
thus S1 = (RingMorphismStr(#G19,G39,g9*f9#)) by A12,A18,A17
.= S2 by A13,A18,A17;
end;
end;
theorem Th5:
G1 <= G2 & G2 <= G3 implies G1 <= G3
proof
assume that
A1: G1 <= G2 and
A2: G2 <= G3;
consider F0 being RingMorphism such that
A3: dom(F0) = G1 and
A4: cod(F0) = G2 by A1;
reconsider F = the RingMorphismStr of F0 as RingMorphism by Lm2;
dom(F) = G1 & cod(F) = G2 by A3,A4;
then reconsider F9 = F as Morphism of G1,G2 by A1,Def8;
consider f being Function of G1,G2 such that
A5: F9 = RingMorphismStr(#G1,G2,f#) by A1,Lm8;
consider G0 being RingMorphism such that
A6: dom(G0) = G2 and
A7: cod(G0) = G3 by A2;
reconsider G = the RingMorphismStr of G0 as RingMorphism by Lm2;
dom(G) = G2 & cod(G) = G3 by A6,A7;
then reconsider G9 = G as Morphism of G2,G3 by A2,Def8;
consider g being Function of G2,G3 such that
A8: G9 = RingMorphismStr(#G2,G3,g#) by A2,Lm8;
dom(G) = cod(F) by A4,A6;
then G*F = RingMorphismStr(#G1,G3,g*f#) by A8,A5,Def9;
then dom(G*F) = G1 & cod(G*F) = G3;
hence thesis;
end;
theorem Th6:
for G being Morphism of G2,G3, F being Morphism of G1,G2 st G1 <=
G2 & G2 <= G3 holds G*F is Morphism of G1,G3
proof
let G be Morphism of G2,G3, F be Morphism of G1,G2;
assume that
A1: G1 <= G2 and
A2: G2 <= G3;
consider g being Function of G2,G3 such that
A3: G = RingMorphismStr(#G2,G3,g#) by A2,Lm8;
consider f being Function of G1,G2 such that
A4: F = RingMorphismStr(#G1,G2,f#) by A1,Lm8;
dom(G) = G2 by A2,Def8
.= cod(F) by A1,Def8;
then G*F = RingMorphismStr(#G1,G3,g*f#) by A3,A4,Def9;
then
A5: dom(G*F) = G1 & cod(G*F) = G3;
G1 <= G3 by A1,A2,Th5;
hence thesis by A5,Def8;
end;
definition
let G1,G2,G3;
let G be Morphism of G2,G3, F be Morphism of G1,G2;
assume
A1: G1 <= G2 & G2 <= G3;
func G*'F -> strict Morphism of G1,G3 equals
:Def10:
G*F;
coherence by A1,Th6;
end;
theorem Th7:
for f,g being strict RingMorphism st dom g = cod f holds ex G1,
G2,G3 st ex f0 being Function of G1,G2, g0 being Function of G2,G3 st f =
RingMorphismStr(#G1,G2,f0#) & g = RingMorphismStr(#G2,G3,g0#) & g*f =
RingMorphismStr(#G1,G3,g0*f0#)
proof
let f,g be strict RingMorphism such that
A1: dom g = cod f;
set G1 = dom f,G2 = cod f, G3 = cod g;
reconsider g9 = g as Morphism of G2,G3 by A1,Th3;
consider g0 being Function of G2,G3 such that
A2: g9 = RingMorphismStr(#G2,G3,g0#) by A1;
reconsider f9 = f as Morphism of G1,G2 by Th3;
consider f0 being Function of G1,G2 such that
A3: f9 = RingMorphismStr(#G1,G2,f0#);
take G1,G2,G3,f0,g0;
thus thesis by A1,A3,A2,Def9;
end;
theorem Th8:
for f,g being strict RingMorphism st dom g = cod f holds dom(g*f
) = dom f & cod (g*f) = cod g
proof
let f,g be strict RingMorphism;
assume dom g = cod f;
then
A1: ex G1,G2,G3 being Ring, f0 being Function of G1,G2, g0 being Function of
G2,G3 st f = RingMorphismStr(#G1,G2,f0#) & g = RingMorphismStr(# G2,G3,g0#) & g
*f = RingMorphismStr(#G1,G3,g0*f0#) by Th7;
hence dom(g*f) = dom f;
thus thesis by A1;
end;
theorem Th9:
for f being Morphism of G1,G2, g being Morphism of G2,G3, h
being Morphism of G3,G4 st G1 <= G2 & G2 <= G3 & G3 <= G4 holds h*(g*f) = (h*g)
*f
proof
let f be Morphism of G1,G2, g be Morphism of G2,G3, h be Morphism of G3,G4;
assume that
A1: G1 <= G2 and
A2: G2 <= G3 and
A3: G3 <= G4;
consider f0 being Function of G1,G2 such that
A4: f = RingMorphismStr(#G1,G2,f0#) by A1,Lm8;
consider h0 being Function of G3,G4 such that
A5: h = RingMorphismStr(#G3,G4,h0#) by A3,Lm8;
consider g0 being Function of G2,G3 such that
A6: g = RingMorphismStr(#G2,G3,g0#) by A2,Lm8;
A7: cod(g) = G3 by A6;
A8: dom(h) = G3 by A5;
then
A9: h*g = RingMorphismStr(#G2,G4,h0*g0#) by A6,A5,A7,Def9;
A10: dom(g) = G2 by A6;
then
A11: dom(h*g) = G2 by A7,A8,Th8;
A12: cod(f) = G2 by A4;
then
A13: cod(g*f) = G3 by A10,A7,Th8;
g*f = RingMorphismStr(#G1,G3,g0*f0#) by A4,A6,A12,A10,Def9;
then h*(g*f) = RingMorphismStr(#G1,G4,h0*(g0*f0)#) by A5,A8,A13,Def9
.= RingMorphismStr(#G1,G4,(h0*g0)*f0#) by RELAT_1:36
.= (h*g)*f by A4,A12,A9,A11,Def9;
hence thesis;
end;
theorem Th10:
for f,g,h being strict RingMorphism st dom h = cod g & dom g =
cod f holds h*(g*f) = (h*g)*f
proof
let f,g,h be strict RingMorphism such that
A1: dom h = cod g and
A2: dom g = cod f;
set G1 = dom f,G2 = cod f, G3 = cod g, G4 = cod h;
reconsider h9 = h as Morphism of G3,G4 by A1,Th3;
reconsider f9 = f as Morphism of G1,G2 by Th3;
reconsider g9 = g as Morphism of G2,G3 by A2,Th3;
A3: G1 <= G2;
G2 <= G3 & G3 <= G4 by A1,A2;
then h9*(g9*f9) = (h9*g9)*f9 by A3,Th9;
hence thesis;
end;
theorem
dom ID(G) = G & cod ID(G) = G & (for f being strict RingMorphism
st cod f = G holds (ID G)*f = f) & for g being strict RingMorphism st dom g = G
holds g*(ID G) = g
proof
set i = ID G;
thus
A1: dom i = G & cod i = G;
thus for f being strict RingMorphism st cod f = G holds i*f = f
proof
let f be strict RingMorphism such that
A2: cod f = G;
set H = dom(f);
reconsider f9 = f as Morphism of H,G by A2,Th3;
consider m being Function of H,G such that
A3: f9 = RingMorphismStr(#H,G,m#) by A2;
(id G)*m = m by FUNCT_2:17;
hence thesis by A1,A2,A3,Def9;
end;
thus for g being strict RingMorphism st dom g = G holds g*(ID G) = g
proof
let f be strict RingMorphism such that
A4: dom f = G;
set H = cod(f);
reconsider f9 = f as Morphism of G,H by A4,Th3;
consider m being Function of G,H such that
A5: f9 = RingMorphismStr(#G,H,m#) by A4;
m*(id G) = m by FUNCT_2:17;
hence thesis by A1,A4,A5,Def9;
end;
end;
::
:: 2. Domains of rings
::
definition
let IT be set;
attr IT is Ring_DOMAIN-like means
:Def11:
for x being Element of IT holds x is strict Ring;
end;
registration
cluster Ring_DOMAIN-like non empty for set;
existence
proof
set X = the strict Ring;
set D = {X};
take D;
for x be Element of D holds x is strict Ring by TARSKI:def 1;
hence thesis;
end;
end;
definition
mode Ring_DOMAIN is Ring_DOMAIN-like non empty set;
end;
reserve V for Ring_DOMAIN;
definition
let V;
redefine mode Element of V -> Ring;
coherence by Def11;
end;
registration
let V;
cluster strict for Element of V;
existence
proof
set e = the Element of V;
e is strict Ring by Def11;
hence thesis;
end;
end;
definition
let IT be set;
attr IT is RingMorphism_DOMAIN-like means
:Def12:
for x being object st x in IT holds x is strict RingMorphism;
end;
registration
cluster RingMorphism_DOMAIN-like for non empty set;
existence
proof
set G = the Ring;
take {ID G};
for x being object st x in {ID G} holds x is strict RingMorphism by
TARSKI:def 1;
hence thesis;
end;
end;
definition
mode RingMorphism_DOMAIN is RingMorphism_DOMAIN-like non empty set;
end;
definition
let M be RingMorphism_DOMAIN;
redefine mode Element of M -> RingMorphism;
coherence by Def12;
end;
registration
let M be RingMorphism_DOMAIN;
cluster strict for Element of M;
existence
proof
set m = the Element of M;
m is strict RingMorphism by Def12;
hence thesis;
end;
end;
theorem Th12:
for f being strict RingMorphism holds {f} is RingMorphism_DOMAIN
proof
let f be strict RingMorphism;
for x being object st x in {f} holds x is strict RingMorphism
by TARSKI:def 1;
hence thesis by Def12;
end;
definition
let G,H;
mode RingMorphism_DOMAIN of G,H -> RingMorphism_DOMAIN means
:Def13:
for x being Element of it holds x is Morphism of G,H;
existence
proof
set F = the Morphism of G,H;
reconsider D = {F} as RingMorphism_DOMAIN by Th12;
take D;
thus thesis by TARSKI:def 1;
end;
end;
theorem Th13:
D is RingMorphism_DOMAIN of G,H iff for x being Element of D
holds x is Morphism of G,H
proof
thus D is RingMorphism_DOMAIN of G,H implies for x being Element of D holds
x is Morphism of G,H by Def13;
thus (for x being Element of D holds x is Morphism of G,H) implies D is
RingMorphism_DOMAIN of G,H
proof
assume
A1: for x being Element of D holds x is Morphism of G,H;
then for x being object st x in D holds x is strict RingMorphism;
then reconsider D9 = D as RingMorphism_DOMAIN by Def12;
for x being Element of D9 holds x is Morphism of G,H by A1;
hence thesis by Def13;
end;
end;
theorem
for f being Morphism of G,H holds {f} is RingMorphism_DOMAIN of G,H
proof
let f be Morphism of G,H;
for x being Element of {f} holds x is Morphism of G,H by TARSKI:def 1;
hence thesis by Th13;
end;
definition
let G,H;
assume
A1: G <= H;
func Morphs(G,H) -> RingMorphism_DOMAIN of G,H means
:Def14:
for x being object holds x in it iff x is Morphism of G,H;
existence
proof
set F = the Morphism of G,H;
set D = { RingMorphismStr(# G,H,f#) where f is Element of Maps(G,H) : f is
linear };
consider f being Function of G,H such that
F = RingMorphismStr(#G,H,f#) and
A2: f is linear by A1,Lm7;
reconsider f0 = f as Element of Maps(G,H) by FUNCT_2:8;
RingMorphismStr(# G,H,f0#) in D by A2;
then reconsider D as non empty set;
A3: for x being object holds x in D implies x is Morphism of G,H
proof let x be object;
assume x in D;
then
ex f being Element of Maps(G,H) st x = RingMorphismStr (#G,H,f#) & f
is linear;
hence thesis by Lm5;
end;
then
A4: for x being Element of D holds x is Morphism of G,H;
A5: for x being object holds x is Morphism of G,H implies x in D
proof let x be object;
assume x is Morphism of G,H;
then reconsider x as Morphism of G,H;
A6: dom(x) = G & cod(x) = H by A1,Def8;
then reconsider f = the Fun of x as Function of G,H;
reconsider g = f as Element of Maps(G,H) by FUNCT_2:8;
A7: x = RingMorphismStr(# G,H,g #) by A6;
(the Fun of x) is linear by Lm3;
hence thesis by A7;
end;
reconsider D as RingMorphism_DOMAIN of G,H by A4,Th13;
take D;
thus thesis by A3,A5;
end;
uniqueness
proof
let D1,D2 be RingMorphism_DOMAIN of G,H such that
A8: for x being object holds x in D1 iff x is Morphism of G,H and
A9: for x being object holds x in D2 iff x is Morphism of G,H;
for x being object holds x in D1 iff x in D2
proof let x be object;
hereby
assume x in D1;
then x is Morphism of G,H by A8;
hence x in D2 by A9;
end;
assume x in D2;
then x is Morphism of G,H by A9;
hence thesis by A8;
end;
hence thesis by TARSKI:2;
end;
end;
definition
let G,H;
let M be RingMorphism_DOMAIN of G,H;
redefine mode Element of M -> Morphism of G,H;
coherence by Def13;
end;
registration
let G,H;
let M be RingMorphism_DOMAIN of G,H;
cluster strict for Element of M;
existence
proof
set e = the Element of M;
e is Morphism of G,H;
hence thesis;
end;
end;
::
:: 4a. Category of rings - objects
::
definition
let x,y be object;
pred GO x,y means
ex x1,x2,x3,x4,x5,x6 being set st x = [[x1,x2,x3,x4],x5,x6] &
ex G being strict Ring st y = G & x1 = the carrier of G & x2 = the
addF of G & x3 = comp G & x4 = 0.G & x5 = the multF of G & x6 = 1.G;
end;
theorem Th15:
for x,y1,y2 being object st GO x,y1 & GO x,y2 holds y1 = y2
proof
let x,y1,y2 be object such that
A1: GO x,y1 and
A2: GO x,y2;
consider a1,a2,a3,a4,a5,a6 being set such that
A3: x = [[a1,a2,a3,a4],a5,a6] and
A4: ex G being strict Ring st y1 = G & a1 = the carrier of G & a2 = the
addF of G & a3 = comp G & a4 = 0.G & a5 = the multF of G & a6 = 1.G by A1;
consider b1,b2,b3,b4,b5,b6 being set such that
A5: x = [[b1,b2,b3,b4],b5,b6] and
A6: ex G being strict Ring st y2 = G & b1 = the carrier of G & b2 = the
addF of G & b3 = comp G & b4 = 0.G & b5 = the multF of G & b6 = 1.G by A2;
consider G2 being strict Ring such that
A7: y2 = G2 and
A8: b1 = the carrier of G2 & b2 = the addF of G2 and
b3 = comp G2 and
A9: b4 = 0.G2 and
A10: b5 = the multF of G2 & b6 = 1.G2 by A6;
consider G1 being strict Ring such that
A11: y1 = G1 and
A12: a1 = the carrier of G1 & a2 = the addF of G1 and
a3 = comp G1 and
A13: a4 = 0.G1 and
A14: a5 = the multF of G1 & a6 = 1.G1 by A4;
A15: the multF of G1 = the multF of G2 & 1.G1 = 1.G2 by A3,A5,A14,A10,
XTUPLE_0:3;
A16: [a1,a2,a3,a4] = [b1,b2,b3,b4] by A3,A5,XTUPLE_0:3;
then
the carrier of G1 = the carrier of G2 & the addF of G1 = the addF of G2
by A12,A8,XTUPLE_0:5;
hence thesis by A11,A13,A7,A9,A16,A15,XTUPLE_0:5;
end;
theorem Th16:
ex x being object st x in UN & GO x,Z_3
proof
set G = Z_3;
reconsider x1 = the carrier of G, x2 = the addF of G, x3 = comp G, x4 = 0.G,
x5 = the multF of G, x6 = 1.G as Element of UN by MOD_2:29;
set x9 = [x1,x2,x3,x4];
set x = [x9,x5,x6];
take x;
x9 is Element of UN by GRCAT_1:1;
hence thesis by GRCAT_1:1;
end;
definition
let UN;
func RingObjects(UN) -> set means
:Def16:
for y being object holds y in it iff ex x st x in UN & GO x,y;
existence
proof
defpred P[object,object] means GO $1,$2;
A1: for x,y1,y2 being object st P[x,y1] & P[x,y2] holds y1 = y2 by Th15;
consider Y being set such that
A2: for y being object holds y in Y iff
ex x being object st x in UN & P[x,y] from TARSKI:sch 1(A1);
take Y;
let y be object;
thus y in Y implies ex x st x in UN & GO x,y
proof assume y in Y;
then ex x being object st x in UN & P[x,y] by A2;
hence thesis;
end;
thus thesis by A2;
end;
uniqueness
proof
let Y1,Y2 be set such that
A3: for y being object holds y in Y1 iff ex x st x in UN & GO x,y and
A4: for y being object holds y in Y2 iff ex x st x in UN & GO x,y;
now
let y be object;
y in Y1 iff ex x st x in UN & GO x,y by A3;
hence y in Y1 iff y in Y2 by A4;
end;
hence thesis by TARSKI:2;
end;
end;
theorem Th17:
Z_3 in RingObjects(UN)
proof
ex x being object st x in UN & GO x,Z_3 by Th16;
hence thesis by Def16;
end;
registration
let UN;
cluster RingObjects(UN) -> non empty;
coherence by Th17;
end;
theorem Th18:
for x being Element of RingObjects(UN) holds x is strict Ring
proof
let x be Element of RingObjects(UN);
consider u being set such that
u in UN and
A1: GO u,x by Def16;
ex x1,x2,x3,x4,x5,x6 being set st u = [[x1,x2,x3,x4],x5,x6] & ex G being
strict Ring st x = G & x1 = the carrier of G & x2 = the addF of G & x3 = comp G
& x4 = 0.G & x5 = the multF of G & x6 = 1.G by A1;
hence thesis;
end;
registration
let UN;
cluster RingObjects(UN) -> Ring_DOMAIN-like;
coherence
by Th18;
end;
::
:: 4b. Category of rings - morphisms
::
definition
let V;
func Morphs(V) -> RingMorphism_DOMAIN means
:Def17:
for x being object holds
x in it iff ex G,H being Element of V st G <= H & x is Morphism of G,H;
existence
proof
set G0 = the Element of V;
set M = Morphs(G0,G0), S = { Morphs(G,H) where G is Element of V, H is
Element of V : G <= H };
(ID(G0)) is Element of M & M in S by Def14;
then reconsider T = union S as non empty set by TARSKI:def 4;
A1: for x being object holds
x in T iff ex G,H being Element of V st G <= H & x is Morphism of G,H
proof let x be object;
thus x in T implies ex G,H being Element of V st G <= H & x is Morphism
of G,H
proof
assume x in T;
then consider Y being set such that
A2: x in Y and
A3: Y in S by TARSKI:def 4;
consider G,H being Element of V such that
A4: Y = Morphs(G,H) and
A5: G <= H by A3;
take G,H;
x is Element of Morphs(G,H) by A2,A4;
hence thesis by A5;
end;
thus (ex G,H being Element of V st G <= H & x is Morphism of G,H)
implies x in T
proof
given G,H being Element of V such that
A6: G <= H & x is Morphism of G,H;
set M = Morphs(G,H);
x in M & M in S by A6,Def14;
hence thesis by TARSKI:def 4;
end;
end;
now
let x be object;
assume x in T;
then ex G,H being Element of V st G <= H & x is Morphism of G,H by A1;
hence x is strict RingMorphism;
end;
then reconsider T9 = T as RingMorphism_DOMAIN by Def12;
take T9;
thus thesis by A1;
end;
uniqueness
proof
let D1,D2 be RingMorphism_DOMAIN such that
A7: for x being object holds
x in D1 iff ex G,H being Element of V st G <= H & x is Morphism of G,H and
A8: for x being object holds
x in D2 iff ex G,H being Element of V st G <= H & x is Morphism of G,H;
now
let x be object;
x in D1 iff ex G,H being Element of V st G <= H & x is Morphism of
G, H by A7;
hence x in D1 iff x in D2 by A8;
end;
hence thesis by TARSKI:2;
end;
end;
::
:: 4c. Category of rings - dom,cod,id
::
definition
let V;
let F be Element of Morphs(V);
redefine func dom(F) -> Element of V;
coherence
proof
consider G,H being Element of V such that
A1: G <= H and
A2: F is Morphism of G,H by Def17;
reconsider F9 = F as Morphism of G,H by A2;
dom(F9) = G by A1,Def8;
hence thesis;
end;
redefine func cod(F) -> Element of V;
coherence
proof
consider G,H being Element of V such that
A3: G <= H and
A4: F is Morphism of G,H by Def17;
reconsider F9 = F as Morphism of G,H by A4;
cod(F9) = H by A3,Def8;
hence thesis;
end;
end;
definition
let V;
let G be Element of V;
func ID(G) -> strict Element of Morphs(V) equals
ID(G);
coherence by Def17;
::$CD
end;
definition
let V;
func dom(V) -> Function of Morphs(V),V means
:Def19:
for f being Element of Morphs(V) holds it.f = dom(f);
existence
proof
deffunc G(Element of Morphs(V))= dom($1);
consider F being Function of Morphs(V),V such that
A1: for f being Element of Morphs(V) holds F.f = G(f) from FUNCT_2:sch
4;
take F;
thus thesis by A1;
end;
uniqueness
proof
let F1,F2 be Function of Morphs(V),V such that
A2: for f being Element of Morphs(V) holds F1.f = dom(f) and
A3: for f being Element of Morphs(V) holds F2.f = dom(f);
now
let f be Element of Morphs(V);
F1.f = dom(f) by A2;
hence F1.f = F2.f by A3;
end;
hence thesis by FUNCT_2:63;
end;
func cod(V) -> Function of Morphs(V),V means
:Def20:
for f being Element of Morphs(V) holds it.f = cod(f);
existence
proof
deffunc G(Element of Morphs(V))=cod($1);
consider F being Function of Morphs(V),V such that
A4: for f being Element of Morphs(V) holds F.f = G(f) from FUNCT_2:sch
4;
take F;
thus thesis by A4;
end;
uniqueness
proof
let F1,F2 be Function of Morphs(V),V such that
A5: for f being Element of Morphs(V) holds F1.f = cod(f) and
A6: for f being Element of Morphs(V) holds F2.f = cod(f);
now
let f be Element of Morphs(V);
F1.f = cod(f) by A5;
hence F1.f = F2.f by A6;
end;
hence thesis by FUNCT_2:63;
end;
::$CD
end;
::
:: 4d. Category of rings - superposition
::
theorem Th19:
for g,f being Element of Morphs(V) st dom(g) = cod(f) ex G1,G2,
G3 being Element of V st G1 <= G2 & G2 <= G3 & g is Morphism of G2,G3 & f is
Morphism of G1,G2
proof
set X = Morphs(V);
defpred P[Element of X,Element of X] means dom($1) = cod($2);
let g,f be Element of X such that
A1: P[g,f];
consider G2,G3 being Element of V such that
A2: G2 <= G3 & g is Morphism of G2,G3 by Def17;
consider G1,G29 being Element of V such that
A3: G1 <= G29 & f is Morphism of G1,G29 by Def17;
A4: G29 = cod(f) by A3,Def8;
G2 = dom(g) by A2,Def8;
hence thesis by A1,A2,A3,A4;
end;
theorem Th20:
for g,f being Element of Morphs(V) st dom(g) = cod(f) holds g*f in Morphs(V)
proof
set X = Morphs(V);
defpred P[Element of X,Element of X] means dom($1) = cod($2);
let g,f be Element of X;
assume P[g,f];
then consider G1,G2,G3 being Element of V such that
A1: G1 <= G2 & G2 <= G3 and
A2: g is Morphism of G2,G3 and
A3: f is Morphism of G1,G2 by Th19;
reconsider f9 = f as Morphism of G1,G2 by A3;
reconsider g9 = g as Morphism of G2,G3 by A2;
G1 <= G3 & g9*'f9 = g9*f9 by A1,Def10,Th5;
hence thesis by Def17;
end;
definition
let V;
func comp(V) -> PartFunc of [:Morphs(V),Morphs(V):],Morphs(V) means
:Def21:
(for g,f being Element of Morphs(V) holds [g,f] in dom it iff dom(g) = cod(f))
& for g,f being Element of Morphs(V) st [g,f] in dom it holds it.(g,f) = g*f;
existence
proof
set X = Morphs(V);
defpred P[Element of X,Element of X] means dom($1) = cod($2);
deffunc F(Element of X,Element of X)=$1*$2;
A1: for g,f being Element of X st P[g,f] holds F(g,f) in X by Th20;
consider c being PartFunc of [:X,X:],X such that
A2: ( for g,f being Element of X holds [g,f] in dom c iff P[g,f])& for
g,f being Element of X st [g,f] in dom c holds c.(g,f) = F(g,f) from BINOP_1:
sch 8(A1);
take c;
thus thesis by A2;
end;
uniqueness
proof
set X = Morphs(V);
defpred P[Element of X,Element of X] means dom($1) = cod($2);
let c1,c2 be PartFunc of [:X,X:],X such that
A3: for g,f being Element of X holds [g,f] in dom c1 iff P[g,f] and
A4: for g,f being Element of X st [g,f] in dom c1 holds c1.(g,f) = g*f and
A5: for g,f being Element of X holds [g,f] in dom c2 iff P[g,f] and
A6: for g,f being Element of X st [g,f] in dom c2 holds c2.(g,f) = g*f;
set V0 = dom c1;
A7: now
let x be object;
assume
A8: x in dom c1;
then consider g,f being Element of X such that
A9: x = [g,f] by SUBSET_1:43;
P[g,f] by A3,A8,A9;
hence x in dom c2 by A5,A9;
end;
then
A10: dom c1 c= dom c2 by TARSKI:def 3;
A11: for x,y being object st [x,y] in V0 holds c1.(x,y)=c2.(x,y)
proof
let x,y be object;
assume
A12: [x,y] in V0;
then reconsider x,y as Element of X by ZFMISC_1:87;
c1.(x,y) = x*y by A4,A12;
hence thesis by A6,A7,A12;
end;
now
let x be object;
assume
A13: x in dom c2;
then consider g,f being Element of X such that
A14: x = [g,f] by SUBSET_1:43;
P[g,f] by A5,A13,A14;
hence x in dom c1 by A3,A14;
end;
then dom c2 c= dom c1 by TARSKI:def 3;
hence thesis by A11,A10,BINOP_1:20,XBOOLE_0:def 10;
end;
end;
::
:: 4e. Definition of Category of rings
::
definition
let UN;
func RingCat(UN) -> CatStr equals
CatStr(#RingObjects UN,Morphs RingObjects UN,
dom RingObjects UN,cod RingObjects UN, comp RingObjects UN#);
coherence;
end;
registration
let UN;
cluster RingCat(UN) -> strict non void non empty;
coherence;
end;
theorem Th21:
for f,g being Morphism of RingCat(UN) holds [g,f] in dom(the
Comp of RingCat(UN)) iff dom g = cod f
proof
set C = RingCat(UN), V = RingObjects(UN);
let f,g be Morphism of C;
reconsider f9 = f as Element of Morphs(V);
reconsider g9 = g as Element of Morphs(V);
dom g = dom(g9) & cod f = cod(f9) by Def19,Def20;
hence thesis by Def21;
end;
theorem Th22:
for f being (Morphism of RingCat(UN)), f9 being Element of
Morphs(RingObjects(UN)), b being Object of RingCat(UN), b9 being Element of
RingObjects(UN) holds f is strict Element of Morphs(RingObjects(UN)) & f9 is
Morphism of RingCat(UN) & b is strict Element of RingObjects(UN) & b9 is Object
of RingCat(UN)
proof
set C = RingCat(UN), V = RingObjects(UN);
set X = Morphs(V);
let f be (Morphism of C), f9 be Element of X, b be Object of C, b9 be
Element of V;
consider x such that
x in UN and
A1: GO x,b by Def16;
ex G,H being Element of V st G <= H & f is Morphism of G,H by Def17;
hence f is strict Element of X;
thus f9 is Morphism of C;
ex x1,x2,x3,x4,x5,x6 being set st x = [[x1,x2,x3,x4],x5,x6] & ex G being
strict Ring st b = G & x1 = the carrier of G & x2 = the addF of G & x3 = comp G
& x4 = 0.G & x5 = the multF of G & x6 = 1.G by A1;
hence b is strict Element of V;
thus thesis;
end;
::$CT
theorem Th23:
for f,g being (Morphism of RingCat(UN)), f9,g9 being Element of
Morphs(RingObjects(UN)) st f = f9 & g = g9 holds (dom g = cod f iff dom g9 =
cod f9) & (dom g = cod f iff [g9,f9] in dom comp(RingObjects(UN))) & (dom g =
cod f implies g(*)f = g9*f9) & (dom f = dom g iff dom f9 = dom g9) &
(cod f = cod
g iff cod f9 = cod g9)
proof
set C = RingCat(UN), V = RingObjects(UN);
set X = Morphs(V);
let f,g be Morphism of C;
let f9,g9 be Element of X;
assume that
A1: f = f9 and
A2: g = g9;
A3: cod f = cod f9 by A1,Def20;
hence dom g = cod f iff dom g9 = cod f9 by A2,Def19;
dom g = dom g9 by A2,Def19;
hence
A4: dom g = cod f iff [g9,f9] in dom comp(V) by A3,Def21;
thus dom g = cod f implies g(*)f = g9*f9
proof
assume
A5: dom g = cod f;
then [g,f] in dom (the Comp of C) by Th21;
hence g(*)f = (comp(V)).(g9,f9) by A1,A2,CAT_1:def 1
.= g9*f9 by A4,A5,Def21;
end;
dom f = dom f9 by A1,Def19;
hence dom f = dom g iff dom f9 = dom g9 by A2,Def19;
cod g = cod g9 by A2,Def20;
hence thesis by A1,Def20;
end;
Lm9: for f,g being Morphism of RingCat(UN) st dom g = cod f
holds dom(g(*)f) = dom f & cod (g(*)f) = cod g
proof
set X = Morphs((RingObjects(UN)));
let f,g be Morphism of (RingCat(UN)) such that
A1: dom g = cod f;
reconsider g9 = g as strict Element of X by Th22;
reconsider f9 = f as strict Element of X by Th22;
A2: dom g9 = cod f9 by A1,Th23;
then reconsider gf = g9*f9 as Element of X by Th20;
A3: gf = g(*)f by A1,Th23;
dom(g9*f9) = dom f9 & cod (g9*f9) = cod g9 by A2,Th8;
hence thesis by A3,Th23;
end;
Lm10: for f,g,h being Morphism of RingCat(UN) st dom h = cod g & dom g = cod f
holds h(*)(g(*)f) = (h(*)g)(*)f
proof
set X = Morphs((RingObjects(UN)));
let f,g,h be Morphism of (RingCat(UN)) such that
A1: dom h = cod g & dom g = cod f;
reconsider f9=f, g9=g, h9=h as strict Element of X by Th22;
A2: h9*g9 = h(*)g & dom(h(*)g) = cod(f) by A1,Lm9,Th23;
A3: dom h9 = cod g9 & dom g9 = cod f9 by A1,Th23;
then reconsider gf = g9*f9, hg = h9*g9 as strict Element of X by Th20;
g9*f9 = g(*)f & dom(h) = cod(g(*)f) by A1,Lm9,Th23;
then h(*)(g(*)f) = h9*gf by Th23
.= hg*f9 by A3,Th10
.= (h(*)g)(*)f by A2,Th23;
hence thesis;
end;
registration
let UN;
cluster RingCat(UN) -> Category-like
transitive associative reflexive;
coherence
proof set C = RingCat UN;
thus C is Category-like
by Th21;
thus C is transitive
by Lm9;
thus C is associative
by Lm10;
thus C is reflexive
proof let a be Element of C;
reconsider G = a as Element of RingObjects UN;
consider x such that
x in UN and
A1: GO x,G by Def16;
set ii = ID G;
consider x1,x2,x3,x4,x5,x6 being set such that
x = [[x1,x2,x3,x4],x5,x6] and
A2: ex H being strict Ring st G = H & x1 = the carrier of H & x2 = the
addF of H & x3 = comp H & x4 = 0.H & x5 = the multF of H & x6 = 1.H
by A1;
reconsider G as strict Element of RingObjects UN by A2;
reconsider ii as Morphism of C;
reconsider ia = ii as RingMorphismStr;
A3: dom ii = dom ia by Def19
.= a;
cod ii = cod ia by Def20
.= a;
then ii in Hom(a,a) by A3;
hence Hom(a,a)<>{};
end;
end;
end;
Lm11:
for a being Element of RingCat UN, aa being Element of RingObjects UN
st a = aa
for i being Morphism of a,a st i = ID aa
for b being Element of RingCat UN holds
(Hom(a,b)<>{} implies for g being Morphism of a,b holds g(*)i = g) &
(Hom(b,a)<>{} implies for f being Morphism of b,a holds i(*)f = f)
proof
let a be Element of RingCat UN,
aa be Element of RingObjects UN such that
a = aa;
let i be Morphism of a,a such that
A1: i = ID aa;
let b be Element of RingCat UN;
thus Hom(a,b)<>{} implies for g being Morphism of a,b holds g(*)i = g
proof assume
A2: Hom(a,b)<>{};
let g be Morphism of a,b;
reconsider gg=g, ii=i as Element of Morphs RingObjects UN;
consider G1,H1 being Element of RingObjects UN such that
A3: G1 <= H1 and
A4: gg is Morphism of G1,H1 by Def17;
consider f being Function of G1,H1 such that
A5: gg = RingMorphismStr(#G1,H1,f#) by A3,A4,Lm8;
A6: Hom(a,a) <> {} by CAT_1:def 9;
A7: dom g = a by A2,CAT_1:5 .= cod i by A6,CAT_1:5;
then
A8: dom gg = cod ii by Th23;
then reconsider f as Function of aa,H1 by A5,A1;
A9: [gg,ii] in dom comp RingObjects UN by Th23,A7;
hence g(*)i
= (comp RingObjects UN).(g,i) by CAT_1:def 1
.= gg*ii by A9,Def21
.= RingMorphismStr(# aa,H1,f*id aa#) by A1,Def9,A5,A8
.= g by A1,A5,A8,FUNCT_2:17;
end;
thus Hom(b,a)<>{} implies for f being Morphism of b,a holds i(*)f = f
proof assume
A10: Hom(b,a)<>{};
let g be Morphism of b,a;
reconsider gg=g, ii=i as Element of Morphs RingObjects UN;
consider G1,H1 being Element of RingObjects UN such that
A11: G1 <= H1 and
A12: gg is Morphism of G1,H1 by Def17;
consider f being Function of G1,H1 such that
A13: gg = RingMorphismStr(#G1,H1,f#) by A11,A12,Lm8;
A14: Hom(a,a) <> {} by CAT_1:def 9;
A15: cod g = a by A10,CAT_1:5 .= dom i by A14,CAT_1:5;
then
A16: cod gg = dom ii by Th23;
reconsider f as Function of G1,aa by A13,A1,A16;
A17: [ii,gg] in dom comp RingObjects UN by A15,Th23;
hence i(*)g = (comp RingObjects UN).(i,g) by CAT_1:def 1
.= ii*gg by A17,Def21
.= RingMorphismStr(# G1,aa,(id aa)*f#) by A1,Def9,A13,A16
.= g by A1,A16,A13,FUNCT_2:17;
end;
end;
registration
let UN;
cluster RingCat(UN) -> with_identities;
coherence
proof set C = RingCat UN;
let a be Element of C;
reconsider aa = a as Element of RingObjects(UN);
reconsider ii = ID aa as Morphism of C;
reconsider ia = ii as RingMorphismStr;
A1: dom ii = dom ia by Def19
.= a;
cod ii = cod ia by Def20
.= a;
then reconsider ii as Morphism of a,a by A1,CAT_1:4;
take ii;
thus thesis by Lm11;
end;
end;
theorem
for a being Object of RingCat(UN), aa being Element of
RingObjects(UN) st a = aa holds id a = ID aa
proof let a be Object of RingCat UN, aa be Element of RingObjects UN;
set C = RingCat UN;
assume
A1: a = aa;
reconsider ii = ID aa as Morphism of C;
reconsider ia = ii as RingMorphismStr;
A2: dom ii = dom ia by Def19
.= a by A1;
cod ii = cod ia by Def20
.= a by A1;
then reconsider ii as Morphism of a,a by A2,CAT_1:4;
for b being Object of C holds
(Hom(a,b) <> {} implies
for f being Morphism of a,b holds f(*)ii = f)
& (Hom(b,a) <> {} implies
for f being Morphism of b,a holds ii(*)f = f) by A1,Lm11;
hence id a = ID aa by CAT_1:def 12;
end;