Echo mates, where squares with the black king are of different colors.
See also: Echo mates.
Grubert, Harald
Schachmaty (Baku), 1990
1st Prize
a) 1.Kf1 S4e6 2.Ke2 Kb4 3.Kd3 Sf4+ 4.Kd4 Sc6# b) 1.Kg2 f4 2.Kf3 Se6 3.Ke4 f3+ 4.Kd5 Sc7#
FEN: 3N4/8/8/1K6/3N4/5P2/5P2/6k1
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