MAYBE

Problem:
 strict:
  b(b(a(a(b(a(b(x1))))))) -> b(a(b(b(a(b(b(x1)))))))
  b(b(b(x1))) -> b(b(a(b(b(x1)))))
 weak:
  b(a(b(x1))) -> b(a(b(a(a(b(x1))))))

Proof:
 Open