What a mate in four puzzle tests
The attacking side has up to four moves to force checkmate. The defender receives three opportunities to alter the position, exchange an attacker, create an escape square, or interrupt the intended line. Every one of those resources has to be considered.
The main difficulty is keeping the idea intact across several branches. A move that looks forcing may place a piece on the wrong square for the final position. Strong solvers connect the beginning of the line to a specific mating picture and check that each intermediate move supports it.
A practical method for four-move lines
Reduce the number of branches before calculating deeply. Start with the king, defenders, and likely mating net.
Map the king's current and potential escape squares, including squares that could open after an exchange.
Identify defenders that can block, capture, or trade the pieces needed for the mating net.
Compare forcing candidates and preparatory moves, giving the opponent the most active response each time.
Follow each surviving branch to the final mate and recheck the exact order from the starting position.
Long-line tactical themes
Clearance can create the route for a rook, bishop, or queen several moves before that piece becomes active. An interference move may then disconnect a defender, while a sacrifice fixes the king on the required square.
Defensive exchanges deserve special attention. If the opponent can trade the main attacker, the remaining pieces must still complete the mating net. Calculate the position after the exchange instead of assuming the attack continues automatically.
End-position rule
Picture the final mate, then ask whether every earlier move preserves the pieces, lines, and tempo needed to reach it.
Test the complete variation
Hold the four-move sequence in mind, choose the strongest defense for Black, and move only when every branch is clear.
Why calculate four moves deep
This depth trains working memory and branch selection. You learn to keep one line accurate while comparing it with a second defensive option, a common demand in tactical game positions.
It also exposes hopeful calculation. If a line depends on a passive reply, the puzzle rejects it immediately and directs attention to the defensive resource that was missed.