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