member x' Cons x xs member[Ite][True][Ite] !EQ x' x x' Cons x xs member x Nil False notEmpty Cons x xs True notEmpty Nil False goal x xs member x xs !EQ S x S y !EQ x y !EQ 0 S y False !EQ S x 0 False !EQ 0 0 True member[Ite][True][Ite] False x' Cons x xs member x' xs member[Ite][True][Ite] True x xs True member 2 !EQ 2 True 0 S 1 Cons 2 member[Ite][True][Ite] 3 Nil 0 0 0 notEmpty 1 goal 2 False 0 INNERMOST