let a, b be Integer; :: thesis: for A1, B1, A2, B2 being sequence of NAT st A1 . 0 = |.a.| & B1 . 0 = |.b.| & ( for i being Nat holds
( A1 . (i + 1) = B1 . i & B1 . (i + 1) = (A1 . i) mod (B1 . i) ) ) & A2 . 0 = |.a.| & B2 . 0 = |.b.| & ( for i being Nat holds
( A2 . (i + 1) = B2 . i & B2 . (i + 1) = (A2 . i) mod (B2 . i) ) ) holds
( A1 = A2 & B1 = B2 )
let A1, B1, A2, B2 be sequence of NAT; :: thesis: ( A1 . 0 = |.a.| & B1 . 0 = |.b.| & ( for i being Nat holds
( A1 . (i + 1) = B1 . i & B1 . (i + 1) = (A1 . i) mod (B1 . i) ) ) & A2 . 0 = |.a.| & B2 . 0 = |.b.| & ( for i being Nat holds
( A2 . (i + 1) = B2 . i & B2 . (i + 1) = (A2 . i) mod (B2 . i) ) ) implies ( A1 = A2 & B1 = B2 ) )
assume A1: ( A1 . 0 = |.a.| & B1 . 0 = |.b.| & ( for i being Nat holds
( A1 . (i + 1) = B1 . i & B1 . (i + 1) = (A1 . i) mod (B1 . i) ) ) ) ; :: thesis: ( not A2 . 0 = |.a.| or not B2 . 0 = |.b.| or ex i being Nat st
( A2 . (i + 1) = B2 . i implies not B2 . (i + 1) = (A2 . i) mod (B2 . i) ) or ( A1 = A2 & B1 = B2 ) )
assume A2: ( A2 . 0 = |.a.| & B2 . 0 = |.b.| & ( for i being Nat holds
( A2 . (i + 1) = B2 . i & B2 . (i + 1) = (A2 . i) mod (B2 . i) ) ) ) ; :: thesis: ( A1 = A2 & B1 = B2 )
defpred S₁[ Nat] means ( A1 . $1 = A2 . $1 & B1 . $1 = B2 . $1 );
A3: S₁[ 0 ] by A1, A2;
A4: for n being Nat st S₁[n] holds
S₁[n + 1]

proof

let n be Nat; :: thesis: ( S₁[n] implies S₁[n + 1] )
assume A5: S₁[n] ; :: thesis: S₁[n + 1]
A6: A1 . (n + 1) = B1 . n by A1
.= A2 . (n + 1) by A2, A5 ;
B1 . (n + 1) = (A1 . n) mod (B1 . n) by A1
.= B2 . (n + 1) by A2, A5 ;
hence S₁[n + 1] by A6; :: thesis: verum

end;

for n being Nat holds S₁[n] from NAT_1:sch 2(A3, A4);
hence ( A1 = A2 & B1 = B2 ) ; :: thesis: verum