(VAR x y )
(RULES 
        f(true,s(x)) -> f(eq(0,minus(x,x)),double(s(x)))
        double(0) -> 0
        double(s(x)) -> s(s(double(x)))
        minus(x,0) -> x
        minus(0,y) -> 0
        minus(s(x),s(y)) -> minus(x,y)
        eq(0,0) -> true
        eq(s(x),0) -> false
        eq(0,s(y)) -> false
        eq(s(x),s(y)) -> eq(x,y)
        
)