const In : set set prop term iIn = In infix iIn 2000 2000 const Inj0 : set set const setsum : set set set axiom Inj0_setsum: !x:set.!y:set.!z:set.z iIn x -> Inj0 z iIn setsum x y const Empty : set axiom Inj0_pair_0_eq: Inj0 = setsum Empty claim !x:set.!y:set.!z:set.z iIn x -> setsum Empty z iIn setsum x y