From: Colin Paul Adams COLINA DEMON CO UK> Date: 3 feb 2000 Subject: CHU: A2 flawed? Nick has created .caf files (the format for mating problems used by my program) for all the A problems. I am working through them to check they are correct. I did not attempt to "solve" A1 with the computer, as a trial suggests it will take many days. But I did have a go at A2. Working through the published solution, and then counting the moves for the Lion mate, it appeared to be mate in 12, so I set the search depth to 24, and gave it a try. To my surprise, after only 37 minutes (I was expecting a few hours), the computer claims that there is no solution. This is supposed to be definitive, but it is of course possible that the program may have a bug (if it fails to generate all possible checks, for instance). As I am due to release this particular version (2.4) with the mating problem solving capability on Saturday, I am anxious to see if this problem is genuinely flawed, or whether it is a bug. Now the computer only gives the moves for the correct solution, so tracking down why it thinks there is no solution can be difficult. So I thought I'd see if I could find a defence myself. My first thought was that White can try K-6b at move 2. I then came up with the following line: 1 +DH 2a - 6a 1 S 5b x 6a 2 Ln 6f - 4e 2 K 6c - 6b 3 Ln 4e - 4c 3 K 6b - 7a 4 Ln 4c x 5c (Ln - 5a is much the same) 4 K 7a - 8b 5 Ln 5c x 6a (+DH x 7c must also be considered here, but I think Ph x 7c is a defence) 5 K 8b - 9b 6 Ln 6a x 7b - 7a 6 K 9b - 10b and no mate. Can people look at this, and see if they can find an improvement for Black? Steve, can you have a look at this with Zillions? -- Colin Paul Adams Preston Lancashire