const Sep : set (set prop) set const nIn : set set prop term setminus = \x:set.\y:set.Sep x \z:set.nIn z y const In : set set prop term iIn = In infix iIn 2000 2000 axiom SepE: !x:set.!p:set prop.!y:set.y iIn Sep x p -> y iIn x & p y claim !x:set.!y:set.!z:set.z iIn setminus x y -> z iIn x & nIn z y