(VAR x y )
(RULES 
        sqr(0) -> 0
        sqr(s(x)) -> +(sqr(x), s(double(x)))
        double(0) -> 0
        double(s(x)) -> s(s(double(x)))
        +(x, 0) -> x
        +(x, s(y)) -> s(+(x, y))
        sqr(s(x)) -> s(+(sqr(x), double(x)))
        
)