# Don't bully your little sister at chess

This puzzle was inspired by @RewanDemontay's puzzle De-zephyr The Solution!. Rewan kindly granted me permission for making this puzzle and citing his as my source of inspiration. I thought of naming it "Zephyr that!" but titles can't be that short on SE.

You're a little girl playing chess with your brother. He knows that you have just learned the rules and he's been toying with you for the whole game, setting up half of his pawns for promotion and getting his pieces into a nice square shape while your king was constantly under checkmate threat. He was hardly paying attention to your moves and didn't see that you were cooking up a little treat of your own.

Please wipe out the entire set of black pieces and deliver checkmate in as few moves as possible.

Your brother is playing optimally and making every move he can to make the game last longer (and of course if you misplay he will not miss an opportunity to win or draw).

Bonus: at some point, your brother grins in delight, thinking you've lost control of the situation. You just captured a rook and four black pieces are left on the board: a pawn, a knight, a queen and the king. You did not choose the shortest way to a complete cleaning of the board, but you are still pretty much in control of the situation. Prove it to him and deliver checkmate to a lone king with your 49th move.

FEN: 1q1N3k/2prN1R1/Kn3Qn1/1p4p1/1r4b1/1p4b1/2pppp2/8 w - - 0 1

• Well that was quick! I'll leave it to others to sovle this one though! ;D Also, my bounty ends in 5 or 6 hours. And some of my questions are still unanswered if you want something to do now... – Rewan Demontay Aug 6 '19 at 13:07
• @RewanDemontay Feel free to try it. Also, you can end your bounty yourself whenever you like. – Arnaud Mortier Aug 6 '19 at 13:17
• The most difficult thing about this problem seems to be finding moves that make progress but don't checkmate the black king... – Gareth McCaughan Aug 7 '19 at 0:21
• @GarethMcCaughan What you shall find the most difficult thing to do will depend on how you tackle the problem. – Arnaud Mortier Aug 7 '19 at 17:44
• Shouldn't it read, "deliver checkmate in as many moves as possible"? (EDIT: No, as both conditions must be met. Whoops.) – Cloudy7 Aug 8 '19 at 3:11

01. Rxg6+ Kh7
02. Qf7+ Kh8
03. Qf8+ Kh7
04. Rg7+ Kh6
05. Nf7+ Kh5
06. Rxg5+ Kh4
07. Qh6+ Bh5
08. Nf5+ Kh3
09. Qxh5+ Kg2
10. Rxg3+ Kf1

(Updated) This time around, the pawns are the obstacle, as they can move forward to defend all while being promoted

What a cruel little sister though, she could have ended his misery with just one move starting with this board !

• rot13(Zbir gra: xvat gnxrf dhrra.) – Arnaud Mortier Aug 8 '19 at 13:27
• The sister is not the cruel one, she's reacting normally to being bullied - ever read Carrie by Stephen King? ;) – Arnaud Mortier Aug 8 '19 at 13:28
• +1, an interesting line. I feel that you could do more in this direction even though it's not the one my solution takes. Don't hesitate to ping me in the comments when you make updates. – Arnaud Mortier Aug 10 '19 at 22:54

My inner little sister can do it in

45 moves.
[FEN "1q1N3k/2prN1R1/Kn3Qn1/1p4p1/1r4b1/1p4b1/2pppp2/8 w - - 0 1"] 1.Rxg6+ Kh7 2.Rg7+ Kh8 3.Rxg5+ Kh7 4.Rg7+ Kh8 5.Rxg4+ Kh7 6.Rg7+ Kh8 7.Rxg3+ Kh7 8.Qf7+ Kh8 9.Qf8+ Kh7 10.Rg7+ Kh6 11.Qf6+ Kh5 12.Qg6+ Kh4 13.Qg5+ Kh3 14.Qh5+ Rh4 15.Qf3+ Kh2 16.Qxf2+ Kh3 17.Qf3+ Kh2 18.Rg2+ Kh1 19.Rxe2+ Kg1 20.Rg2+ Kh1 21.Rxd2+ Kg1 22.Rg2+ Kh1 23.Rxc2+ Kg1 24.Qf2+ Kh1 25.Qxh4+ Kg1 26.Qg3+ Kh1 27.Qh3+ Kg1 28.Rg2+ Kf1 29.Qf3+ Ke1 30.Qf2+ Kd1 31.Qe2+ Kc1 32.Qe1+ Rd1 33.Qc3+ Kb1 34.Qxb3+ Ka1 35.Qc3+ Kb1 36.Rb2+ Ka1 37.Rxb5+ Ka2 38.Rb2+ Ka1 39.Rxb6+ ( 39.Rd2+ Kb1 40.Rxd1+ Ka2 41.Rd2+ Kb1 42.Rb2+ Ka1 43.Rxb6+ Ka2 44.Qc2+ Ka1 45.Qd1+ Ka2 46.Rxb8 Ka3 47.Qc1+ Ka2 48.Qxc7 Ka3 49.Qa5# ) 39...Ka2 40.Qb3+ Ka1 41.Qxd1+ Ka2 42.Rxb8 Ka3 43.Qc1+ Ka4 44.Qxc7 Ka3 45.Qa5# *

Replay

Not sure this is optimal, though. Bonus answer is given as a variation.

• Very nice! I actually don't have a formal proof that this is optimal but it is indeed the intended solution. If no one can find better, the bounty is yours. – Arnaud Mortier Mar 22 at 8:46