isEmpty cons x xs false isEmpty nil true isZero 0 true isZero s x false head cons x xs x tail cons x xs xs tail nil nil p s s x s p s x p s 0 0 p 0 0 inc s x s inc x inc 0 s 0 sumList xs y if isEmpty xs isZero head xs y tail xs cons p head xs tail xs inc y if true b y xs ys x y if false true y xs ys x sumList xs y if false false y xs ys x sumList ys x sum xs sumList xs 0 isEmpty 1 cons 2 false 0 nil 0 true 0 isZero 1 0 0 s 1 head 1 tail 1 p 1 inc 1 sumList 2 if 6 sum 1 INNERMOST ./TRS/secret06/aprove/sumList.trs