Mainplan: -1.f5xe5 e.p. e7-e5 -2.Rd3-b3 and forward 1.Rd8# but -1…e7-e5 and 1...O-O#! as a forward defense. Dual free both in White’s play and Black’s refutation, notice that White cannot uncapture any Black piece on its second retraction.
Solution: -1.g5xh5 e.p.! h7-h5 -2.f5xe5 e.p. e7-e5 (O-O#? but illegal!: the bPs have captured all missing white units, including wPs d2,e2, and f2, so one of them must have promoted by crossing d7 or f7, thus Black has lost the right to castle) -3.Rd3-b3 and forward 1.Rd8#
Description: Logical Proca retractor with Black castling as a forward defense requiring a foreplan to prevent Black castling.
Comments: An old Frolkin idea of using the forward defence as the hidden theme, enhanced here by an e.p. capture prior to the e.p. capture which is really needed to get the solution (Roberto Osorio).
