In the Philidor position you defend against rook and pawn with your king in front of the pawn. Keep your rook on your third rank, so the enemy king can't come forward. The only way to try for more is to push the pawn onto that rank, but then the king has no shelter in front of its pawn. At that moment, drop your rook to the far end of the board and check from behind. The king can't escape the checks without leaving the pawn.
Every move is checked with an endgame tablebase, which knows the exact result of every position with up to seven pieces. The computer defends perfectly, and if a move throws the result away, the trainer stops and shows you a better one.
