isvalid

When state A is active, receive message M. If the message has a data value equal to 3, discard the message. Then, when state B is active, check that the message M is still valid. If the message is valid and has a data value equal to 6, discard the message.

In state A:

during:
   if receive(M) == true
      if M.data == 3
         discard(M);
      end
   end

In state B:

during:
   if isvalid(M) == true
      if M.data == 6
         discard(M);
      end
   end