let n be non empty Nat; :: thesis: for J being non empty non void Signature

for T being non-empty MSAlgebra over J

for X being V3() GeneratorSet of T

for S1 being non empty non void b_{1} -extension n PC-correct QC-correct QCLangSignature over Union X

for x, y being Element of Union X

for x0, y0 being Element of Union (X extended_by ({}, the carrier of S1))

for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let J be non empty non void Signature; :: thesis: for T being non-empty MSAlgebra over J

for X being V3() GeneratorSet of T

for S1 being non empty non void J -extension n PC-correct QC-correct QCLangSignature over Union X

for x, y being Element of Union X

for x0, y0 being Element of Union (X extended_by ({}, the carrier of S1))

for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let T be non-empty MSAlgebra over J; :: thesis: for X being V3() GeneratorSet of T

for S1 being non empty non void J -extension n PC-correct QC-correct QCLangSignature over Union X

for x, y being Element of Union X

for x0, y0 being Element of Union (X extended_by ({}, the carrier of S1))

for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let X be V3() GeneratorSet of T; :: thesis: for S1 being non empty non void J -extension n PC-correct QC-correct QCLangSignature over Union X

for x, y being Element of Union X

for x0, y0 being Element of Union (X extended_by ({}, the carrier of S1))

for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let S1 be non empty non void J -extension n PC-correct QC-correct QCLangSignature over Union X; :: thesis: for x, y being Element of Union X

for x0, y0 being Element of Union (X extended_by ({}, the carrier of S1))

for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let x, y be Element of Union X; :: thesis: for x0, y0 being Element of Union (X extended_by ({}, the carrier of S1))

for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let x0, y0 be Element of Union (X extended_by ({}, the carrier of S1)); :: thesis: for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let L be non-empty Language of X extended_by ({}, the carrier of S1),S1; :: thesis: for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let G1 be QC-theory_with_equality of L; :: thesis: for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let A be Formula of L; :: thesis: for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let s be SortSymbol of S1; :: thesis: ( L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite implies \for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1 )

set Y = X extended_by ({}, the carrier of S1);

assume that

A0: ( L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct ) and

A1: ( x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite ) ; :: thesis: \for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

A2: ( s in dom X & dom X = the carrier of J ) by A1, FUNCT_1:def 2, PARTFUN1:def 2;

then ( X . s c= the Sorts of T . s & the Sorts of T . s = the Sorts of L . s ) by Th16, PBOOLE:def 2, PBOOLE:def 18;

then reconsider t1 = x0, t2 = y0 as Element of L,s by A1;

reconsider j = s as SortSymbol of J by A2;

reconsider q1 = t1, q2 = t2 as Element of T,j by Th16;

A3: (t2 '=' (t1,L)) \imp (((A / (x0,y0)) / (y0,t2)) \imp ((A / (x0,y0)) / (y0,t1))) in G1 by A1, Def42;

(t1 '=' (t2,L)) \imp (t2 '=' (t1,L)) in G1 by A0, A1, A2, ThOne;

then A8: (t1 '=' (t2,L)) \imp (((A / (x0,y0)) / (y0,t2)) \imp ((A / (x0,y0)) / (y0,t1))) in G1 by A3, Th45;

dom (X extended_by ({}, the carrier of S1)) = the carrier of S1 by PARTFUN1:def 2;

then A4: ( X . s = (X extended_by ({}, the carrier of S1)) . s & the Sorts of L . the formula-sort of S1 <> {} & X extended_by ({}, the carrier of S1) is ManySortedSubset of the Sorts of L ) by A2, Th1, Th23;

then A5: (A / (x0,y0)) / (y0,t1) = (A / (x0,y0)) / (y0,x0) by A1, Th14

.= A by A0, A1, A4 ;

A6: (A / (x0,y0)) / (y0,t2) = (A / (x0,y0)) / (y0,y0) by A1, A4, Th14

.= A / (x0,y0) by A0, A1, A4 ;

((t1 '=' (t2,L)) \imp ((A / (x0,y0)) \imp A)) \imp (((t1 '=' (t2,L)) \and (A / (x0,y0))) \imp A) in G1 by Th48;

then ((t1 '=' (t2,L)) \and (A / (x0,y0))) \imp A in G1 by A8, A5, A6, Def38;

then ( \for (y,(((t1 '=' (t2,L)) \and (A / (x0,y0))) \imp A)) in G1 & (\for (y,(((t1 '=' (t2,L)) \and (A / (x0,y0))) \imp A))) \imp ((\ex (y,((t1 '=' (t2,L)) \and (A / (x0,y0))))) \imp A) in G1 ) by A0, A1, A2, Th120, Def39;

then A9: (\ex (y,((t1 '=' (t2,L)) \and (A / (x0,y0))))) \imp A in G1 by Def38;

B1: (((t1 '=' (t2,L)) \and (A / (x0,y0))) / (y0,x0)) \imp (\ex (y,((t1 '=' (t2,L)) \and (A / (x0,y0))))) in G1 by A0, A1, A2, Th110;

vf t1 = s -singleton x0 by A0, A1;

then (vf t1) . s = {x0} by AOFA_A00:6;

then B2: y0 nin (vf t1) . s by A1, TARSKI:def 1;

B3: ((t1 '=' (t2,L)) \and (A / (x0,y0))) / (y0,x0) = ((t1 '=' (t2,L)) / (y0,x0)) \and ((A / (x0,y0)) / (y0,x0)) by A0, A1, A4, Th27

.= ((t1 '=' (t2,L)) / (y0,x0)) \and A by A0, A1, A4

.= ((t1 '=' (t2,L)) / (y0,t1)) \and A by A1, A4, Th14

.= ((t1 / (y0,t1)) '=' ((t2 / (y0,t1)),L)) \and A by A0, A1

.= (t1 '=' ((t2 / (y0,t1)),L)) \and A by B2, A0, A1, A4

.= (t1 '=' (t1,L)) \and A by A0, A1, A4 ;

q1 '=' (q1,L) in G1 by Def42;

then ( A \imp (t1 '=' (t1,L)) in G1 & A \imp A in G1 ) by Th34, Th44;

then A \imp ((t1 '=' (t1,L)) \and A) in G1 by Th201;

then A \imp (\ex (y,((t1 '=' (t2,L)) \and (A / (x0,y0))))) in G1 by B1, B3, Th45;

then A \iff (\ex (y,((t1 '=' (t2,L)) \and (A / (x0,y0))))) in G1 by A9, Th43;

hence \for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1 by A1, Def39; :: thesis: verum

for T being non-empty MSAlgebra over J

for X being V3() GeneratorSet of T

for S1 being non empty non void b

for x, y being Element of Union X

for x0, y0 being Element of Union (X extended_by ({}, the carrier of S1))

for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let J be non empty non void Signature; :: thesis: for T being non-empty MSAlgebra over J

for X being V3() GeneratorSet of T

for S1 being non empty non void J -extension n PC-correct QC-correct QCLangSignature over Union X

for x, y being Element of Union X

for x0, y0 being Element of Union (X extended_by ({}, the carrier of S1))

for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let T be non-empty MSAlgebra over J; :: thesis: for X being V3() GeneratorSet of T

for S1 being non empty non void J -extension n PC-correct QC-correct QCLangSignature over Union X

for x, y being Element of Union X

for x0, y0 being Element of Union (X extended_by ({}, the carrier of S1))

for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let X be V3() GeneratorSet of T; :: thesis: for S1 being non empty non void J -extension n PC-correct QC-correct QCLangSignature over Union X

for x, y being Element of Union X

for x0, y0 being Element of Union (X extended_by ({}, the carrier of S1))

for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let S1 be non empty non void J -extension n PC-correct QC-correct QCLangSignature over Union X; :: thesis: for x, y being Element of Union X

for x0, y0 being Element of Union (X extended_by ({}, the carrier of S1))

for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let x, y be Element of Union X; :: thesis: for x0, y0 being Element of Union (X extended_by ({}, the carrier of S1))

for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let x0, y0 be Element of Union (X extended_by ({}, the carrier of S1)); :: thesis: for L being non-empty Language of X extended_by ({}, the carrier of S1),S1

for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let L be non-empty Language of X extended_by ({}, the carrier of S1),S1; :: thesis: for G1 being QC-theory_with_equality of L

for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let G1 be QC-theory_with_equality of L; :: thesis: for A being Formula of L

for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let A be Formula of L; :: thesis: for s being SortSymbol of S1 st L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite holds

\for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

let s be SortSymbol of S1; :: thesis: ( L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct & x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite implies \for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1 )

set Y = X extended_by ({}, the carrier of S1);

assume that

A0: ( L is subst-correct3 & L is vf-finite & L is subst-correct2 & L is subst-correct & L is subst-eq-correct & L is vf-qc-correct & L is vf-eq-correct ) and

A1: ( x = x0 & x0 in X . s & y = y0 & y0 in X . s & x <> y & y nin (vf A) . s & X . s is infinite ) ; :: thesis: \for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1

A2: ( s in dom X & dom X = the carrier of J ) by A1, FUNCT_1:def 2, PARTFUN1:def 2;

then ( X . s c= the Sorts of T . s & the Sorts of T . s = the Sorts of L . s ) by Th16, PBOOLE:def 2, PBOOLE:def 18;

then reconsider t1 = x0, t2 = y0 as Element of L,s by A1;

reconsider j = s as SortSymbol of J by A2;

reconsider q1 = t1, q2 = t2 as Element of T,j by Th16;

A3: (t2 '=' (t1,L)) \imp (((A / (x0,y0)) / (y0,t2)) \imp ((A / (x0,y0)) / (y0,t1))) in G1 by A1, Def42;

(t1 '=' (t2,L)) \imp (t2 '=' (t1,L)) in G1 by A0, A1, A2, ThOne;

then A8: (t1 '=' (t2,L)) \imp (((A / (x0,y0)) / (y0,t2)) \imp ((A / (x0,y0)) / (y0,t1))) in G1 by A3, Th45;

dom (X extended_by ({}, the carrier of S1)) = the carrier of S1 by PARTFUN1:def 2;

then A4: ( X . s = (X extended_by ({}, the carrier of S1)) . s & the Sorts of L . the formula-sort of S1 <> {} & X extended_by ({}, the carrier of S1) is ManySortedSubset of the Sorts of L ) by A2, Th1, Th23;

then A5: (A / (x0,y0)) / (y0,t1) = (A / (x0,y0)) / (y0,x0) by A1, Th14

.= A by A0, A1, A4 ;

A6: (A / (x0,y0)) / (y0,t2) = (A / (x0,y0)) / (y0,y0) by A1, A4, Th14

.= A / (x0,y0) by A0, A1, A4 ;

((t1 '=' (t2,L)) \imp ((A / (x0,y0)) \imp A)) \imp (((t1 '=' (t2,L)) \and (A / (x0,y0))) \imp A) in G1 by Th48;

then ((t1 '=' (t2,L)) \and (A / (x0,y0))) \imp A in G1 by A8, A5, A6, Def38;

then ( \for (y,(((t1 '=' (t2,L)) \and (A / (x0,y0))) \imp A)) in G1 & (\for (y,(((t1 '=' (t2,L)) \and (A / (x0,y0))) \imp A))) \imp ((\ex (y,((t1 '=' (t2,L)) \and (A / (x0,y0))))) \imp A) in G1 ) by A0, A1, A2, Th120, Def39;

then A9: (\ex (y,((t1 '=' (t2,L)) \and (A / (x0,y0))))) \imp A in G1 by Def38;

B1: (((t1 '=' (t2,L)) \and (A / (x0,y0))) / (y0,x0)) \imp (\ex (y,((t1 '=' (t2,L)) \and (A / (x0,y0))))) in G1 by A0, A1, A2, Th110;

vf t1 = s -singleton x0 by A0, A1;

then (vf t1) . s = {x0} by AOFA_A00:6;

then B2: y0 nin (vf t1) . s by A1, TARSKI:def 1;

B3: ((t1 '=' (t2,L)) \and (A / (x0,y0))) / (y0,x0) = ((t1 '=' (t2,L)) / (y0,x0)) \and ((A / (x0,y0)) / (y0,x0)) by A0, A1, A4, Th27

.= ((t1 '=' (t2,L)) / (y0,x0)) \and A by A0, A1, A4

.= ((t1 '=' (t2,L)) / (y0,t1)) \and A by A1, A4, Th14

.= ((t1 / (y0,t1)) '=' ((t2 / (y0,t1)),L)) \and A by A0, A1

.= (t1 '=' ((t2 / (y0,t1)),L)) \and A by B2, A0, A1, A4

.= (t1 '=' (t1,L)) \and A by A0, A1, A4 ;

q1 '=' (q1,L) in G1 by Def42;

then ( A \imp (t1 '=' (t1,L)) in G1 & A \imp A in G1 ) by Th34, Th44;

then A \imp ((t1 '=' (t1,L)) \and A) in G1 by Th201;

then A \imp (\ex (y,((t1 '=' (t2,L)) \and (A / (x0,y0))))) in G1 by B1, B3, Th45;

then A \iff (\ex (y,((t1 '=' (t2,L)) \and (A / (x0,y0))))) in G1 by A9, Th43;

hence \for (x,(A \iff (\ex (y,((x '=' (y,L)) \and (A / (x0,y0))))))) in G1 by A1, Def39; :: thesis: verum