Selfmate in 3

After the key 1.Qh6!, which creates a zugzwang, Black has just three possible moves, each uniquely countered by the B+R battery on c3-h8:

• 1...Rxh6 2.Rd7+! Rf6 3.Bxg2—now, with the black rook on the f-file, the only legal options, Rxg2 and Qxg2, both deliver mate to the white king.

• 1...Rh5 2.Rg4+! Re5 3.Rxg3—here, with the black rook guarding e3, the only legal move, Nxg3, results in mate.

• Likewise, 1...Rh4 2.Rd3+! Rd4 3.a5 leads to 3…cxd3#

In each variation, White's battery is activated, fixing Black's mobile rook on a square from where it covers the white king’s escape.

Note that 1.Qf7? is a try that fails only to 1…Rxh7!