10

The heavy door to the Cryostasis Chamber hisses open, releasing a gust of icy air. Inside, a cylindrical pod glows faintly, frost clinging to its surface. Santa lies within, perfectly still, his iconic suit faintly illuminated by the chamber’s light.

Wesley peers closer. "He’s still frozen... but look at this." He points to a tangle of wires dangling from the pod’s control panel. Several components appear dislodged, and a small tool rests nearby, as if someone had been tampering with it.

David’s face darkens. "This wasn’t an accident. Someone’s been here."

Magnus narrows his eyes. "Grinchuk?"

"Possibly," David replies, carefully inspecting the damage. "If this isn’t fixed, the chamber could fail entirely. Santa would get stuck in his frozen state."

Wesley frowns. "Can we fix it?"

David nods. "We have to. But we’ll need to reroute power and recalibrate the system. The first step is to find a way to checkmate Black here."

This is a helpmate problem, which means that both players cooperate to achieve mate.

With Black to move first, how can White, with Black's assistance, mate on the fourth move? Black plays 4 moves and White 4, and White's 4th move is mate.

Please go to the Lichess analysis board, carry out the moves, and copy the PGN under the board. Make sure there are no alternative variants in the PGN before you copy (no parentheses). Remember that since Black starts, the PGN notation on Lichess will say "5." in front of White's 4th move (format: 1... B 2. WB 3. WB 4. WB 5. W). If you're confused about anything, join our Discord server.