isort Cons x xs r isort xs insert x r insert x' Cons x xs insert[Ite][False][Ite] < x' x x' Cons x xs isort Nil r r insert x Nil Cons x Nil inssort xs isort xs Nil < S x S y < x y < 0 S y True < x 0 False insert[Ite][False][Ite] False x' Cons x xs Cons x insert x' xs insert[Ite][False][Ite] True x r Cons x r insert 2 True 0 insert[Ite][False][Ite] 3 < 2 S 1 Cons 2 Nil 0 0 0 isort 2 inssort 1 False 0 INNERMOST