CHESSDORRAMate in 2
White to move
Solution
One solution line: Rxf7+ Ke8 Re7#.
Position analysis
What happens on the board after the solution.
The key idea
Rxf7+ Ke8 Re7# The king on e8 is in check from rook e7, bishop g6. Its own pieces occupy d8, f8. The other escape squares are covered: d7 — rook e7, e7 — queen g7, f7 — rook e7. No legal capture or block removes the check. It is checkmate. Every defense and mating continuation: Rxf7 → Qxf7#; Ke8 → Rxf8# / Re7#.
How to find checkmate
Check the king’s escape squares and every available defense.
When check becomes checkmate
Checkmate occurs when the king is in check and its side has no legal move. With no legal move and no check, the result is stalemate.
Three ways to defend
First check whether the king can move to a safe square. Then look for a legal capture of the checking piece or a block. A knight check cannot be blocked. In double check, only a king move can get out of check.
Mate against every reply
For mate in two, choose a first move, list the opponent’s replies, and find a mate after each. The first move can be quiet. A quiet move leaving the opponent with no legal reply produces stalemate.
Sources
Check and king safety
How to identify check and test the legality of a reply.
King safety after a move
Check your own king after the move you are considering. A pawn can leave a file and expose its king to a rook check even if the king was safe before the move.
Pinned pieces
A pinned piece still attacks squares according to its movement rules. Count those attacks when testing a king move or castling.
Reading the line of check
Locate the checking piece first. If the check travels along a line, test whether it can be blocked. Then check captures and king moves.
Sources
Double check
Two pieces attack the king at the same time.
Check and an opened line
One way to give double check is to move a piece off the line of your rook, bishop, or queen. If the moving piece also attacks the king, both pieces give check at once.
What to check in reply
Only a king move can answer double check. The king may capture one of the checking pieces if the capture square is safe. If there is no safe king move, it is mate.
Sources
Sources · Lichess