let x, y be set ; :: thesis: for A being Ordinal holds
( ( x in Rank A & y in Rank A ) iff {x,y} in Rank (succ A) )
let A be Ordinal; :: thesis: ( ( x in Rank A & y in Rank A ) iff {x,y} in Rank (succ A) )
A1: ( ( x in Rank A & y in Rank A ) iff {x,y} c= Rank A ) by ZFMISC_1:38;
thus ( ( x in Rank A & y in Rank A ) iff {x,y} in Rank (succ A) ) by A1, Th36; :: thesis: verum