Clearance to guard escape square (1 move)
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Explanation
In discovered checkmate, and in discovered check into checkmate, you have seen how to move one piece and give a check with another piece to force a checkmate. Often the moving piece is used to guard an escape square.
In clearance to guard an escape square the roles are reversed: You move one piece, and that move clears the way for another piece to guard an escape square. This is especially strong if the move is a forcing move, such as a check.
In this first level the puzzles are checkmate in one move. Let's look at some examples.
Examples
White can checkmate with 1.Be5#. The bishop gives check and clears the way for the rook to guard the escape squares on the b-file.
White can checkmate with 1.Nxf6#. The bishop gives check and clears the way for the bishop to guard the escape square f7. The e-pawn cannot capture the knight because it is pinned by the rook on e1.
Black can checkmate with 1...c1=N#. The pawn promotes to a knight which gives check, and clears the way for the black rook to guard the escape square d2.