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