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