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This week’s problem is a fine example of an idea known as arrival correction, which will be explained with the solution. The solver should examine closely the positive and negative effects present in the four main defences to the threat.
1.Sb6 threatens 2.Qb4, and four defences interpose at d4. 1...Qd4 selfblocks, and is met by 2.Qc6. 1...Bd4 also selfblocks, but corrects by opening a rook guard on c6. The new error is interference with the black queen, allowing 2.Qd5. 1...Sfd4 again selfblocks but prevents 2.Qc6 by a direct guard. It also interferes with the queen, but corrects by opening a rook guard of d5. The new error is interference with the bishop, allowing 2.Rxc3. Finally 1...Sbd4 repeats the previous negative and positive effects (selfblock corrected by guard of c6, interference on the queen corrected by the opening of a bishop guard on d5 and interference on the bishop corrected by the opening of the bishop guard on c4) but commits a new error of clearing the b-file, allowing 2.b4. This accumulation of effects shows 4th degree arrival correction. There is one by-play variation 1...Qxd7+ 2.Sxd7.
Any comments or questions on this problem should be addressed to
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