last nil 0 last cons x nil x last cons x cons y xs last cons y xs del x nil nil del x cons y xs if eq x y x y xs if true x y xs xs if false x y xs cons y del x xs eq 0 0 true eq 0 s y false eq s x 0 false eq s x s y eq x y reverse nil nil reverse cons x xs cons last cons x xs reverse del last cons x xs cons x xs 2.2 reverse cons x xs reverse del last cons x xs cons x xs if false x y xs del x xs last cons x cons y xs last cons y xs del x cons y xs if eq x y x y xs eq s x s y eq x y reverse cons x xs del last cons x xs cons x xs reverse cons x xs last cons x xs del x cons y xs eq x y reverse cons x xs last cons x xs true reverse cons x xs reverse del last cons x xs cons x xs true Failed! NaTT certifiable-1.6