Tricky puzzle. Great illustration that no game is over.
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Black has some better options on move 4, though. Like this one:
4...Rhf8 5. Qg1/h1 (5. Rxb4 axb4 6. a3/4 b3 7. cxb3 cxb3 8. Qxf3 (8. anything else Rf1+ Qxf1 or blocks 9. Rxf1 or queen#) Rxf3 9. a5 Rf1#) Qxb1+ 6. Qxb1 Rf1 7. a3 Rxb1+ 8. Kxb1 Rf1+ 9. Ka2 Rc1 10. a4 (anything) 11. Ka3 Ra1#
Thanks...that was fun to analyze!!
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