MAYBE

Problem:
 app(app(neq(),0()),0()) -> false()
 app(app(neq(),0()),app(s(),y)) -> true()
 app(app(neq(),app(s(),x)),0()) -> true()
 app(app(neq(),app(s(),x)),app(s(),y)) -> app(app(neq(),x),y)
 app(app(filter(),f),nil()) -> nil()
 app(app(filter(),f),app(app(cons(),y),ys)) ->
 app(app(app(filtersub(),app(f,y)),f),app(app(cons(),y),ys))
 app(app(app(filtersub(),true()),f),app(app(cons(),y),ys)) ->
 app(app(cons(),y),app(app(filter(),f),ys))
 app(app(app(filtersub(),false()),f),app(app(cons(),y),ys)) -> app(app(filter(),f),ys)
 nonzero() -> app(filter(),app(neq(),0()))

Proof:
 Open