Its a simple guessing number game, also known as Bulls and Cows. Try to guess the four non-repeated numbers by the hint of "A"(Bulls - numbers and location matched), or "B"( Crows - numbers matched only).
This game provides single user mode as well as the multiplayer mode which players can compete for the answers with 2 devices over Wifi/Bluetooth. It can search match via GameCenter with friends or online users.
The rule for multiplayer mode is very easy as single player. Each player comes with 3 chances to guess the final answer. The answers can be guessed and submitted any time without order, but you cannot guess more after used up your chances. A new guess number will be generated by devices in the beginning of the game and when time out if no one guesses a new number.
Enjoy and choose the strategy wisely.