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