let A be Euclidean preIfWhileAlgebra; :: thesis: for X being non empty countable set
for b being Element of X
for g being Euclidean ExecutionFunction of A, Funcs X,INT ,(Funcs X,INT ) \ b,0
for x, y, z being Variable of g st ex d being Function st
( d . b = 0 & d . x = 1 & d . y = 2 & d . z = 3 ) holds
for s being Element of Funcs X,INT
for n, m being Element of NAT st n = s . x & m = s . y & n > 0 holds
(g . s,(while (y gt 0 ),((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)))) . x = n gcd m
let X be non empty countable set ; :: thesis: for b being Element of X
for g being Euclidean ExecutionFunction of A, Funcs X,INT ,(Funcs X,INT ) \ b,0
for x, y, z being Variable of g st ex d being Function st
( d . b = 0 & d . x = 1 & d . y = 2 & d . z = 3 ) holds
for s being Element of Funcs X,INT
for n, m being Element of NAT st n = s . x & m = s . y & n > 0 holds
(g . s,(while (y gt 0 ),((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)))) . x = n gcd m
let b be Element of X; :: thesis: for g being Euclidean ExecutionFunction of A, Funcs X,INT ,(Funcs X,INT ) \ b,0
for x, y, z being Variable of g st ex d being Function st
( d . b = 0 & d . x = 1 & d . y = 2 & d . z = 3 ) holds
for s being Element of Funcs X,INT
for n, m being Element of NAT st n = s . x & m = s . y & n > 0 holds
(g . s,(while (y gt 0 ),((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)))) . x = n gcd m
let g be Euclidean ExecutionFunction of A, Funcs X,INT ,(Funcs X,INT ) \ b,0 ; :: thesis: for x, y, z being Variable of g st ex d being Function st
( d . b = 0 & d . x = 1 & d . y = 2 & d . z = 3 ) holds
for s being Element of Funcs X,INT
for n, m being Element of NAT st n = s . x & m = s . y & n > 0 holds
(g . s,(while (y gt 0 ),((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)))) . x = n gcd m
set h = g;
set S = Funcs X,INT ;
set T = (Funcs X,INT ) \ b,0 ;
A1: g complies_with_if_wrt (Funcs X,INT ) \ b,0 by AOFA_000:def 32;
let x, y, z be Variable of g; :: thesis: ( ex d being Function st
( d . b = 0 & d . x = 1 & d . y = 2 & d . z = 3 ) implies for s being Element of Funcs X,INT
for n, m being Element of NAT st n = s . x & m = s . y & n > 0 holds
(g . s,(while (y gt 0 ),((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)))) . x = n gcd m )
given d being Function such that A2: d . b = 0 and
A3: d . x = 1 and
A4: d . y = 2 and
A5: d . z = 3 ; :: thesis: for s being Element of Funcs X,INT
for n, m being Element of NAT st n = s . x & m = s . y & n > 0 holds
(g . s,(while (y gt 0 ),((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)))) . x = n gcd m
set C = y gt 0 ;
let s be Element of Funcs X,INT ; :: thesis: for n, m being Element of NAT st n = s . x & m = s . y & n > 0 holds
(g . s,(while (y gt 0 ),((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)))) . x = n gcd m
A6: y <> z by A4, A5;
reconsider s1 = g . s,(y gt 0 ) as Element of Funcs X,INT ;
A7: s1 . x = s . x by A2, A3, Th38;
A8: s1 . y = s . y by A2, A4, Th38;
A9: ( s . y <= 0 implies s1 . b = 0 ) by Th38;
defpred S₁[ Element of Funcs X,INT ] means ( $1 . x > 0 & $1 . y > 0 );
let n, m be Element of NAT ; :: thesis: ( n = s . x & m = s . y & n > 0 implies (g . s,(while (y gt 0 ),((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)))) . x = n gcd m )
defpred S₂[ Element of Funcs X,INT ] means ( n gcd m divides $1 . x & n gcd m divides $1 . y & $1 . x > 0 & $1 . y >= 0 & ( for c being Nat st c divides $1 . x & c divides $1 . y holds
c divides n gcd m ) );
set J = if-then (z lt 0 ),(z *= (- 1));
set I = (((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z);
assume that
A10: n = s . x and
A11: m = s . y and
A12: n > 0 ; :: thesis: (g . s,(while (y gt 0 ),((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)))) . x = n gcd m
( s . y > 0 implies s1 . b = 1 ) by Th38;
then ( s1 in (Funcs X,INT ) \ b,0 iff S₁[s1] ) by A10, A12, A9, Th2, Th38;
then A13: g iteration_terminates_for ((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)) \; (y gt 0 ),g . s,(y gt 0 ) by A2, A3, A4, A5, A10, A11, A12, A7, A8, Lm2;
A14: z <> x by A3, A5;
A15: x <> y by A3, A4;

A16: now

let s be Element of Funcs X,INT ; :: thesis: ( (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . x = s . y & (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . y = abs ((s . x) - (s . y)) )
set s1 = g . s,(z := ((. x) - (. y)));
set s2 = g . (g . s,(z := ((. x) - (. y)))),(z lt 0 );
set q = g . (g . s,(z := ((. x) - (. y)))),(if-then (z lt 0 ),(z *= (- 1)));
set qz = g . (g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )),(z *= (- 1));
A17: ((g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )) . z) * (- 1) = - ((g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )) . z) ;
set s3 = g . (g . (g . s,(z := ((. x) - (. y)))),(if-then (z lt 0 ),(z *= (- 1)))),(x := y);
set s4 = g . (g . (g . (g . s,(z := ((. x) - (. y)))),(if-then (z lt 0 ),(z *= (- 1)))),(x := y)),(y := z);
A18: g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)) = g . (g . s,(((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y))),(y := z) by AOFA_000:def 29
.= g . (g . (g . s,((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1))))),(x := y)),(y := z) by AOFA_000:def 29
.= g . (g . (g . (g . s,(z := ((. x) - (. y)))),(if-then (z lt 0 ),(z *= (- 1)))),(x := y)),(y := z) by AOFA_000:def 29 ;
( (g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )) . b = 1 implies g . (g . s,(z := ((. x) - (. y)))),(z lt 0 ) in (Funcs X,INT ) \ b,0 ) ;
then A19: ( (g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )) . b = 1 implies g . (g . s,(z := ((. x) - (. y)))),(if-then (z lt 0 ),(z *= (- 1))) = g . (g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )),(z *= (- 1)) ) by A1, AOFA_000:def 30;
A20: (. x) . s = s . x by Th22;
A21: (g . (g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )),(z *= (- 1))) . y = (g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )) . y by A6, Th31;
A22: (. y) . s = s . y by Th22;
((. x) - (. y)) . s = ((. x) . s) - ((. y) . s) by Def11;
then A23: (g . s,(z := ((. x) - (. y)))) . z = (s . x) - (s . y) by A20, A22, Th26;
A24: ( (g . s,(z := ((. x) - (. y)))) . z < 0 implies (g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )) . b = 1 ) by Th38;
A25: (g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )) . z = (g . s,(z := ((. x) - (. y)))) . z by A2, A5, Th38;
A26: (g . (g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )),(z *= (- 1))) . z = ((g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )) . z) * (- 1) by Th31;
A27: (g . (g . (g . s,(z := ((. x) - (. y)))),(if-then (z lt 0 ),(z *= (- 1)))),(x := y)) . z = (g . (g . s,(z := ((. x) - (. y)))),(if-then (z lt 0 ),(z *= (- 1)))) . z by A14, Th27;
A28: (g . (g . (g . (g . s,(z := ((. x) - (. y)))),(if-then (z lt 0 ),(z *= (- 1)))),(x := y)),(y := z)) . y = (g . (g . (g . s,(z := ((. x) - (. y)))),(if-then (z lt 0 ),(z *= (- 1)))),(x := y)) . z by Th27;
( (g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )) . b = 0 implies g . (g . s,(z := ((. x) - (. y)))),(z lt 0 ) nin (Funcs X,INT ) \ b,0 ) by Th2;
then A29: ( (g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )) . b = 0 implies g . (g . s,(z := ((. x) - (. y)))),(if-then (z lt 0 ),(z *= (- 1))) = g . (g . s,(z := ((. x) - (. y)))),(z lt 0 ) ) by A1, AOFA_000:80;
A30: ( (g . s,(z := ((. x) - (. y)))) . z >= 0 implies (g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )) . b = 0 ) by Th38;
A31: (g . s,(z := ((. x) - (. y)))) . y = s . y by A6, Th26;
A32: (g . (g . (g . s,(z := ((. x) - (. y)))),(if-then (z lt 0 ),(z *= (- 1)))),(x := y)) . x = (g . (g . s,(z := ((. x) - (. y)))),(if-then (z lt 0 ),(z *= (- 1)))) . y by Th27;
(g . (g . s,(z := ((. x) - (. y)))),(z lt 0 )) . y = (g . s,(z := ((. x) - (. y)))) . y by A2, A4, Th38;
hence ( (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . x = s . y & (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . y = abs ((s . x) - (s . y)) ) by A15, A29, A19, A25, A24, A30, A21, A26, A17, A18, A31, A23, A32, A27, A28, Th27, ABSVALUE:def 1; :: thesis: verum

end;

A33: for s being Element of Funcs X,INT st S₂[s] & s in (Funcs X,INT ) \ b,0 & S₁[s] holds
S₂[g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))]

proof

let s be Element of Funcs X,INT ; :: thesis: ( S₂[s] & s in (Funcs X,INT ) \ b,0 & S₁[s] implies S₂[g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))] )
reconsider s99 = g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)) as Element of Funcs X,INT ;
A34: abs (n gcd m) = n gcd m by ABSVALUE:def 1;
A35: s99 . y = abs ((s . x) - (s . y)) by A16;
assume A36: S₂[s] ; :: thesis: ( not s in (Funcs X,INT ) \ b,0 or not S₁[s] or S₂[g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))] )
then reconsider n9 = s . x, m9 = s . y as Element of NAT by INT_1:16;
assume that
s in (Funcs X,INT ) \ b,0 and
A37: S₁[s] ; :: thesis: S₂[g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))]
n gcd m divides n9 - m9 by A36, PREPOWER:108;
hence ( n gcd m divides (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . x & n gcd m divides (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . y & (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . x > 0 & (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . y >= 0 ) by A16, A36, A37, A35, A34, INT_2:21; :: thesis: for c being Nat st c divides (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . x & c divides (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . y holds
c divides n gcd m
let c be Nat; :: thesis: ( c divides (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . x & c divides (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . y implies c divides n gcd m )
reconsider c9 = c as Element of NAT by ORDINAL1:def 13;
assume that
A38: c divides (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . x and
A39: c divides (g . s,((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) . y ; :: thesis: c divides n gcd m
A40: abs c = c by ABSVALUE:def 1;
A41: s99 . x = s . y by A16;
c9 divides abs (n9 - m9) by A16, A39;
then A42: c divides n9 - m9 by A40, INT_2:21;
c divides m9 by A16, A38;
then c divides (n9 - m9) + m9 by A42, WSIERP_1:9;
hence c divides n gcd m by A36, A41, A38; :: thesis: verum

end;

A43: for s being Element of Funcs X,INT st S₂[s] holds
( S₂[g . s,(y gt 0 )] & ( g . s,(y gt 0 ) in (Funcs X,INT ) \ b,0 implies S₁[g . s,(y gt 0 )] ) & ( S₁[g . s,(y gt 0 )] implies g . s,(y gt 0 ) in (Funcs X,INT ) \ b,0 ) )

proof

let s be Element of Funcs X,INT ; :: thesis: ( S₂[s] implies ( S₂[g . s,(y gt 0 )] & ( g . s,(y gt 0 ) in (Funcs X,INT ) \ b,0 implies S₁[g . s,(y gt 0 )] ) & ( S₁[g . s,(y gt 0 )] implies g . s,(y gt 0 ) in (Funcs X,INT ) \ b,0 ) ) )
assume A44: S₂[s] ; :: thesis: ( S₂[g . s,(y gt 0 )] & ( g . s,(y gt 0 ) in (Funcs X,INT ) \ b,0 implies S₁[g . s,(y gt 0 )] ) & ( S₁[g . s,(y gt 0 )] implies g . s,(y gt 0 ) in (Funcs X,INT ) \ b,0 ) )
reconsider s9 = g . s,(y gt 0 ) as Element of Funcs X,INT ;
A45: s9 . y = s . y by A2, A4, Th38;
s9 . x = s . x by A2, A3, Th38;
hence S₂[g . s,(y gt 0 )] by A44, A45; :: thesis: ( g . s,(y gt 0 ) in (Funcs X,INT ) \ b,0 iff S₁[g . s,(y gt 0 )] )
A46: ( s . y <= 0 implies s9 . b = 0 ) by Th38;
( s . y > 0 implies s9 . b = 1 ) by Th38;
hence ( g . s,(y gt 0 ) in (Funcs X,INT ) \ b,0 iff S₁[g . s,(y gt 0 )] ) by A44, A46, Th2, Th38; :: thesis: verum

end;

reconsider fin = g . s,(while (y gt 0 ),((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z))) as Element of Funcs X,INT ;
A47: S₂[s] by A10, A11, A12, NAT_D:def 5;
A48: ( S₂[g . s,(while (y gt 0 ),((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)))] & not S₁[g . s,(while (y gt 0 ),((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)))] ) from AOFA_000:sch 5(A47, A13, A33, A43);
then reconsider fn = fin . x as Element of NAT by INT_1:16;
A49: fn divides 0 by NAT_D:6;
fin . y = 0 by A48;
then fn divides n gcd m by A48, A49;
hence (g . s,(while (y gt 0 ),((((z := ((. x) - (. y))) \; (if-then (z lt 0 ),(z *= (- 1)))) \; (x := y)) \; (y := z)))) . x = n gcd m by A48, NAT_D:5; :: thesis: verum