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 term nIn = \x:set.\y:set.~ x iIn y const ordsucc : set set var x:set var f:set set var y:set var z:set hyp !w:set.w iIn ordsucc (ordsucc x) -> !u:set.u iIn ordsucc (ordsucc x) -> f w = f u -> w = u hyp y iIn ordsucc (ordsucc x) hyp f y = x hyp z iIn ordsucc x hyp f z = x claim y = z -> Subq y z