const ordinal : set prop const SNo : set prop axiom ordinal_SNo: !x:set.ordinal x -> SNo x const add_SNo : set set set term + = add_SNo infix + 2281 2280 const ordsucc : set set lemma !x:set.!y:set.ordinal x -> ordinal y -> SNo y -> SNo x -> x + ordsucc y = ordsucc (x + y) var x:set var y:set hyp ordinal x hyp ordinal y claim SNo y -> x + ordsucc y = ordsucc (x + y)