(VAR sum x y z )
(RULES 
        gt(0, y) -> false
        gt(s(x), 0) -> true
        gt(s(x), s(y)) -> gt(x, y)
        plus(0, y) -> y
        plus(s(x), y) -> s(plus(x, y))
        double(0) -> 0
        double(s(x)) -> s(s(double(x)))
        average(x, y) -> aver(plus(x, y), 0)
        aver(sum, z) -> if(gt(sum, double(z)), sum, z)
        if(true, sum, z) -> aver(sum, s(z))
        if(false, sum, z) -> z
        
)