Two pieces of the same colour both stand on any line of the board. A is the front piece, and B the rear piece in one direction. They change position such that 1) A becomes the rear piece, and B becomes the front piece, and then again such that 2) A again becomes the front piece, and B the rear.
See also: Double transposition of two pieces on one line (by Zlatko Mihajloski & Zoran Gavrilovski).
Mihajloski, Zlatko
Abdurahmanović, Fadil
SuperProblem, 2015
1st-2nd Prize
1.Be3
Bf2
2.g5
Kf1
3.g4
Ke2
4.g3
Be1
5.g2
Bd2
6.g1=S+
Kd1
7.Se2
Kc2
8.Sc3
Bc1
9.Sa2
Bb2#
Mihajloski, Zlatko
Abdurahmanović, Fadil
StrateGems, 2011
1st Prize
1...Ba3
2.Sd7
Bd6
3.Sf6
Bxe5
4.Bb4+
Kf4
5.Bf8
Kg5
6.Bg7
Kg6
7.Sg8
Bxg7#