An endgame position Rook+Bishop vs Two Knights
The following diagram shows a position from the very interesting and complicated endgame type Rook+Bishop vs two Knights. Black to move is winning in less than 50 moves...
White is trying to build a fortress. The two knights are connected, thus defending each other, and the black king cannot move closer, since there is a virtual barrier: f5-f4-f3-g3
This is a usual set up for the side having the 2 knights. Other good defensive set ups involve the knights placed diagonally or laterally on adjacent squares, or those where the knights manage to tactically fork a piece.
The only move that wins within 50-moves is 1…Re4!
With all other moves, black would need, according to the Nalimov endgame tablebase, around 80 moves to mate….
The reason for the rook move is, that it attacks both knights at the same time, also maintaining control over the e-file!
White must play 2.Kd1, since other moves lose very quickly material, for example: 2.Ke1 Bxe2 3.Nxe2 Kf3 -+
The next move is 2…Kh3! The black king makes a side step, thus going round the barrier of the knights.
The game could continue with 3.Kd2 (a waiting move, hoping to keep up the fortress) 3…Kg2 4.Kd1 Kf2. The black king couldn’t be stop from entering, and white loses one of the knights.