dec Cons Nil Nil Nil dec Cons Nil Cons x xs dec Cons x xs dec Cons Cons x xs Nil dec Nil dec Cons Cons x' xs' Cons x xs dec Cons x xs isNilNil Cons Nil Nil True isNilNil Cons Nil Cons x xs False isNilNil Cons Cons x xs Nil False isNilNil Cons Cons x' xs' Cons x xs False nestdec Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Nil nestdec Cons x xs nestdec dec Cons x xs number17 n Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Cons Nil Nil goal x nestdec x dec 1 Cons 2 Nil 0 isNilNil 1 True 0 False 0 nestdec 1 number17 1 goal 1 INNERMOST