Day 11 - Retractor

David examines the console, his expression tense. “Rerouting the power didn’t work. Santa really isn’t supposed to wake up for another two weeks. The cryo-systems are programmed for a gradual thaw, perfectly timed for the 24th.”

Magnus frowns. “But with the tampering, waiting isn’t an option, is it?”

David shakes his head. “No. If we don’t get him out of there now, he may never awaken. We’ll have to wake him early this year.”

David starts typing commands into the console. “This won’t be a full wake-up yet, but we’ll begin the thawing sequence. Once the chamber adjusts to normal conditions, we’ll bring him out.”

The chamber hums softly as warm air circulates, frost slowly retreating from the glass. Santa’s figure remains motionless inside, the rhythmic pulsing of the console lights the only sign that the process has begun.

David steps back, watching the frost slowly melt. “Now we wait. This is going to take a couple of hours.”

Magnus settles into a chair nearby. “Well, while we’re waiting, let’s keep our minds sharp. Let’s try to solve this chess problem.”

In the current position, White has just completed a move. First, retract the last move made by White, followed by retracting the last move made by Black. Then, resume the game by making a legal move for Black, and finally, a move for White. White’s last move should deliver checkmate. This is a help-retractor, so both players cooperate.

You do not need to provide the two retracted half-moves in the solution, only the two moves being played forward after the retraction. First a Black move, then a White move, delivering checkmate.