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