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After finding the checkmate, you turn back to David. "Please continue."

David gestures towards a large map on the wall, where pins and threads connect locations across the North Pole. Each pin marks a place where the mysterious letters and chess problems were found. "This map tracks Grinchuk's movements and the chess problems you've faced," he says. "We couldn't let you face Grinchuk alone. Ringing the church bell were our way of redirecting you here. We needed to bring you into the group. You're not just solving puzzles, you're helping us safeguard Christmas!"

The group of elves around you nod in agreement. "Grinchuk is dangerous," David continues. "He's a master of deception, using chess as a tool for his dark schemes. We barely won that last encounter 100 years ago."

"Tomorrow morning, we head to Santa's Workshop," he continues. "We'll need lots of chess gear for what's coming."

Everyone understands the importance of the plan. You settle down for the night in the cabin. When you finally fall asleep, a chess problem forms in your dreams.

With Black to move first, how can White (with Black's assistance) mate on the fifth move (Black plays 5 moves and White 5, and White's fifth move is mate)? Here's a link to the position on Lichess, and here's Offerspill's Discord server.