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  1. Subscriber moonbus
    21 Jan '17 19:11
    mate in two. (White is moving up the board.) PM me your solution.

    Your first instinct will mate, but not in two. Think again, harder.
  2. Standard member krieghoff
    Carrobie was here
    22 Jan '17 03:24
    1. b8=N : a6 (forced 2. Nxc6 ++
  3. Subscriber moonbus
    22 Jan '17 08:13
    Well done! Thank you for all of your replies; there were more than I could reply to personally due to a PM limit (spam filter!) at RHP. The First Responders were:

    robbebop (1588)

    vandervelde (2116)

    Eladar (1499

    thaughbaer (1779)

    HikaruShindo (1661)

    krieghoff (2421)

    I suppose krieghoff and vandervelde saw this instantly. For the rest of us no-where-near-IM-level duffers, I offer the following explanation, what my thought process was in solving this.

    The puzzle intrigued me because it is an example of Emanuel Lasker's remark that when you see a good move, wait, keep looking because you might find something better. My first instinct, and maybe yours too, was to promote the b-pawn to a queen. Black then plays Ka6 and will be mated, eventually, but not on the next move.

    So, I had to think again, harder, and under-promote (an interesting topic in itself).

    At this point, I stopped thinking about what White could move and started thinking about Black instead. The Black K is very nearly stalemated already: he has only one legal square left, a6. Take away a6, and any check will be checkmate. Under-promoting to a N on b8 would take away a6 from the Black K; now a quick look is needed to ensure that Black still has a legal move if a N is on b8 — we don't want to stalemate him. Yes, Black can still play a7-a6 — as krieghoff noted above, forced. This is good, because it traps the Black K, and now any check at all will be checkmate.

    From here, it is a short hop to seeing that Nxc6 is mate.
  4. 22 Jan '17 18:02
    One interesting thing is that I had a different when solving the problem. I looked at promotion to a queen, and then checkmate after 1…a6. It was only as I checked that I realized Black had 1…Ka6. From there, though, I found the knight promotion almost immediately, and checked it several times before sending a pm (not wanting to be wrong.) I think it's a symptom of a larger tendency where I miss moves a lot (even OTB, when I take my time more.)
  5. 23 Jan '17 13:51
    In a game situation I would have gone with the queen just because it was safer without calculating. I don't trust my calculations without a constant check because I am hardly ever correct when trying to calculate.
  6. Subscriber moonbus
    24 Jan '17 08:11
    Good point. Calculation is error prone. GMs play more on general principles than on long I-go-here-you-go-there-I-go-here-you-go-there calculations. How not to calculate would be a good topic for a blog.