(VAR L X XS Y YS )
(RULES 
        app(nil, YS) -> YS
        app(cons(X, XS), YS) -> cons(X, app(XS, YS))
        from(X) -> cons(X, from(s(X)))
        zWadr(nil, YS) -> nil
        zWadr(XS, nil) -> nil
        zWadr(cons(X, XS), cons(Y, YS)) -> cons(app(Y, cons(X, nil)), zWadr(XS, YS))
        prefix(L) -> cons(nil, zWadr(L, prefix(L)))
        
)