A helpmate is a type of chess problem in which both sides cooperate in order to achieve the goal of checkmating Black. In a helpmate in n moves, Black moves first, then White, each side moving n times, to culminate in White's nth move checkmating Black. (In a helpmate in two for example, sometimes abbreviated h#2, the solution consists of a Black move, a White move, a second Black move, then a second White move, giving checkmate.) Although the two sides cooperate, all moves must be legal according to the rules of chess.