No.1724 (JQ)

(C+ Popeye 4.87)

This is a quadruple Grimshaw incorporating an English Grimshaw (line-pinned rook), a pawn Grimshaw, and a vertically moving rook. Three out of four interferences work with additional black errors. Both pawn and Rf4 control f5, which needs a nightrider to pass through for checkmate. After 1...Ref6, shutting off the pawn, white removes the rook with 2.gxf4, discovering mate by QN(e2)-g3-f5-h6 This dual is avoided after 1...Bf6 with the now unpinned rook defending with 2...Rxe2!

Unfortunately the key only provokes the interferences.

Version (without promoted rook, not preferred): Remove Rd6, Pc5
Add Qa6, Bc8 (dummy to close line QN(a7)-c8-d6-f7)