13

Easy illegality is easy: not exactly 1 king on both sides, both kings in check, pawns on the final ranks. It's also fairly easy to tally promoted material and subtract the missing pawns. A quick captures test, together with the pawn structures, is also possible. An impossibility of last move test, even if only cursorily, is already tricky. A full test is NP-...


5

The answer was given in a comment: After your Qa5+ how do you make White play Kf1? What do you do if he plays Qd2? This is correct. There's really nothing you can do after Qa5+ Qd2 that gives Black a significant advantage. He can play Qd2 after Bxa3; Nxa3 Qa5; too right? White can play that, but it doesn't help in that position. You can take the knight ...


4

The knight is pinned to the bishop so when white plays e5 the knight can't move without losing the bishop. It looks like maybe the knight could move to d5 protecting the bishop. The problem is that white can take the knight with the knight on c3 and black doesn't have time to play BxB because the white knight on d5 is threatening the queen on c7 and so black ...


3

OK, so after a bit more research I have concluded that this variation is in fact playable for White, even with perfect play from Black! Here's my analysis: The critical line is [FEN ""] 1.Nc3 d5 2.e4 d4 3.Nce2 e5 4.Ng3 Be6 5.Nf3 f6 6.c3 In this position, we're threatening to win a pawn with 7.cxd4 exd4 8.Qa4+ Nc6 9.Bb5. Black has a couple of ways ...


2

The opening 1.Nc3 is much better than people think, and I have had very good results with it, especially if I pick the opponent. The perfect choice is someone strong enough to try and refute it but not strong enough to do so. The line you mention with 4..Be6 is the only line that worries me, but it only appears if Black is either very well informed or else ...


2

Since this position has less than 6 pieces, the full checkmating line can be produced with the Shredder's online 6 piece DTM tablespace. Here is the full checkmating line that I obtained by playing through it. [FEN "8/5p2/5k2/8/3K2p1/6P1/8/8 w - - 0 1"] 1. Kd5 Kf5 2. Kd4 Ke6 3. Ke4 f5+ 4. Kf4 Kf6 5. Ke3 Ke5 6. Kd3 f4 7. Ke2 f3+ 8. Ke1 f2+ 9. Kxf2 ...


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