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