Solution
Michel Caillaud diagrammes, 1979 Ded. G. Yacoubian
5+10. shc#15 (Consequent Series-Helpmate in 15 moves)
The try 1. Ra3 2. Rxb3?? 3. Rb5 4. Bb4 5-7. Kc4 8. Rc5 9. b5 b3# fails because Wh. has no last move after 2. Rxb3.
The solution is to first capture the wh. Pg2 so that the White King has -1. Kg2-h1 as a possible last move. 1. Rf8 2. Rf2 3. Rxg2!! 4. Rf2 5. Rf8 6. Ra8 and we go on as in the try.