Test your chess: Reitstein problem 20

Black to play and win

White's last move was Rb4*b7; how does black defeat it?

Solution

The solution is easy if you see it- I saw it immediately- or hard: if the latter, Purdy's maxim to examine all biffs again comes to the rescue, with 1…Rb5! having the main purpose of freeing the way for Qd2+, mating.

Another way of seeing it, perhaps, is to apply another of his maxims, to examine all jump checks or jump biffs. I have normally taken that maxim to mean jumping over an enemy piece, but I guess could equally apply to jumping over one of your own pieces: here the jump check Qd8-d2 would then be seen, and from there, the notion of clearing the d line would emerge.

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