const SNo : set prop const Empty : set axiom SNo_0: SNo Empty const mul_SNo : set set set term * = mul_SNo infix * 2291 2290 axiom mul_SNo_zeroR: !x:set.SNo x -> x * Empty = Empty axiom mul_SNo_com: !x:set.!y:set.SNo x -> SNo y -> x * y = y * x claim !x:set.SNo x -> Empty * x = Empty