let x, y, c be set ; :: thesis: for S being non empty ManySortedSign st S = BitAdderWithOverflowStr x,y,c holds
( x in the carrier of S & y in the carrier of S & c in the carrier of S )
set S1 = 2GatesCircStr x,y,c,'xor' ;
let S be non empty ManySortedSign ; :: thesis: ( S = BitAdderWithOverflowStr x,y,c implies ( x in the carrier of S & y in the carrier of S & c in the carrier of S ) )
assume A1: S = BitAdderWithOverflowStr x,y,c ; :: thesis: ( x in the carrier of S & y in the carrier of S & c in the carrier of S )
A2: c in the carrier of (2GatesCircStr x,y,c,'xor' ) by Th60;
( x in the carrier of (2GatesCircStr x,y,c,'xor' ) & y in the carrier of (2GatesCircStr x,y,c,'xor' ) ) by Th60;
hence ( x in the carrier of S & y in the carrier of S & c in the carrier of S ) by A1, A2, Th20; :: thesis: verum