(VAR x1 )
(RULES 
        b(b(x1)) -> c(d(x1))
        c(c(x1)) -> d(d(d(x1)))
        c(x1) -> g(x1)
        d(d(x1)) -> c(f(x1))
        d(d(d(x1))) -> g(c(x1))
        f(x1) -> a(g(x1))
        g(x1) -> d(a(b(x1)))
        g(g(x1)) -> b(c(x1))
        
)