const In : set set prop term iIn = In infix iIn 2000 2000 const Subq : set set prop term TransSet = \x:set.!y:set.y iIn x -> Subq y x term nIn = \x:set.\y:set.~ x iIn y term ordinal = \x:set.TransSet x & !y:set.y iIn x -> TransSet y const Empty : set axiom EmptyE: !x:set.nIn x Empty axiom FalseE: ~ False claim TransSet Empty & !x:set.x iIn Empty -> TransSet x