(VAR p x xs y ys )
(RULES 
        app(app(app(if,true),xs),ys) -> xs
        app(app(app(if,false),xs),ys) -> ys
        app(app(sub,x),0) -> x
        app(app(sub,app(s,x)),app(s,y)) -> app(app(sub,x),y)
        app(app(gtr,0),y) -> false
        app(app(gtr,app(s,x)),0) -> true
        app(app(gtr,app(s,x)),app(s,y)) -> app(app(gtr,x),y)
        app(app(d,x),0) -> true
        app(app(d,app(s,x)),app(s,y)) -> app(app(app(if,app(app(gtr,x),y)),false),app(app(d,app(s,x)),app(app(sub,y),x)))
        app(len,nil) -> 0
        app(len,app(app(cons,x),xs)) -> app(s,app(len,xs))
        app(app(filter,p),nil) -> nil
        app(app(filter,p),app(app(cons,x),xs)) -> app(app(app(if,app(p,x)),app(app(cons,x),app(app(filter,p),xs))),app(app(filter,p),xs))
        
)