(VAR f x xs y )
(RULES 
        app(app(le,0),y) -> true
        app(app(le,app(s,x)),0) -> false
        app(app(le,app(s,x)),app(s,y)) -> app(app(le,x),y)
        app(pred,app(s,x)) -> x
        app(app(minus,x),0) -> x
        app(app(minus,x),app(s,y)) -> app(pred,app(app(minus,x),y))
        app(app(gcd,0),y) -> y
        app(app(gcd,app(s,x)),0) -> app(s,x)
        app(app(gcd,app(s,x)),app(s,y)) -> app(app(app(if_gcd,app(app(le,y),x)),app(s,x)),app(s,y))
        app(app(app(if_gcd,true),app(s,x)),app(s,y)) -> app(app(gcd,app(app(minus,x),y)),app(s,y))
        app(app(app(if_gcd,false),app(s,x)),app(s,y)) -> app(app(gcd,app(app(minus,y),x)),app(s,x))
        app(app(map,f),nil) -> nil
        app(app(map,f),app(app(cons,x),xs)) -> app(app(cons,app(f,x)),app(app(map,f),xs))
        app(app(filter,f),nil) -> nil
        app(app(filter,f),app(app(cons,x),xs)) -> app(app(app(app(filter2,app(f,x)),f),x),xs)
        app(app(app(app(filter2,true),f),x),xs) -> app(app(cons,x),app(app(filter,f),xs))
        app(app(app(app(filter2,false),f),x),xs) -> app(app(filter,f),xs)
        
)