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 Empty : set const Inj1 : set set axiom Inj1I1: !x:set.Empty iIn Inj1 x const Inj0 : set set axiom Inj0_0: Inj0 Empty = Empty const ordsucc : set set var x:set var y:set hyp y iIn ordsucc Empty claim y = Empty -> Inj0 y iIn Inj1 x