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