(VAR x y )
(RULES 
        double(x) -> plus(x,x)
        double(0) -> 0
        double(s(x)) -> s(s(double(x)))
        plus(0,y) -> y
        plus(s(x),y) -> s(plus(x,y))
        minus(s(x),s(y)) -> minus(x,y)
        minus(0,x) -> 0
        minus(x,0) -> x
        div(s(x),s(y)) -> s(div(minus(s(x),double(s(y))),s(y)))
        div(0,s(y)) -> 0
        
)