r xs ys zs nil xs r xs nil zs cons w ws r xs xs cons succ zero zs ws r xs cons y ys nil cons w ws r xs xs cons succ zero nil ws r xs cons y ys cons z zs cons w ws r ys cons y ys zs cons succ zero cons w ws 2.2 r xs cons y ys nil cons w ws r xs xs cons succ zero nil ws r xs cons y ys cons z zs cons w ws r ys cons y ys zs cons succ zero cons w ws r xs nil zs cons w ws r xs xs cons succ zero zs ws true r xs nil zs cons w ws r xs xs cons succ zero zs ws r xs cons y ys cons z zs cons w ws r ys cons y ys zs cons succ zero cons w ws r xs cons y ys nil cons w ws r xs xs cons succ zero nil ws true Failed! NaTT certifiable-1.6