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 binunion : set set set const omega : set const Repl : set (set set) set const minus_SNo : set set term - = minus_SNo term int = binunion omega (Repl omega minus_SNo) axiom binunionI1: !x:set.!y:set.!z:set.z iIn x -> z iIn binunion x y claim !x:set.x iIn omega -> x iIn int