(VAR x y )
(RULES 
        f(c(s(x),y)) -> f(c(x,s(y)))
        f(c(s(x),s(y))) -> g(c(x,y))
        g(c(x,s(y))) -> g(c(s(x),y))
        g(c(s(x),s(y))) -> f(c(x,y))
        rand(x) ->= x
        rand(x) ->= rand(s(x))
)