This week, we return to the helpmate, with a very nice effort by the current
Vice-President of the BCPS. Remember that, in a helpmate, Black moves first!
1.Qf4 Bc2 2. d2 Bb3+ 3. Kd3 Ba2 4. Qc4 Bb1#.
The black pieces change places: the pawn takes the queen's square, the queen the king's
and the king the pawn's. Meanwhile, White's bishop must unguard and then re-guard the
mating square d3, but it also has to lose a tempo in order to do so, in order to allow
enough time for the black regrouping. This explains the need for the bishop's Rundlauf,
or round trip, going from b1–c2-b3-a2-b1.