const In : set set prop term iIn = In infix iIn 2000 2000 term Subq = \x:set.\y:set.!z:set.z iIn x -> z iIn y const UPair : set set set axiom UPairI1: !x:set.!y:set.x iIn UPair x y const ordsucc : set set const Empty : set var x:set hyp x iIn ordsucc Empty claim x = Empty -> x iIn UPair Empty (ordsucc Empty)