Pb 5 : give the key, the possible threats, all the variations up to and including the fourth white move (reminder: in reverse, white plays and forces black to checkmate him ... a bit masochistic, but good ...)
Ch. Feather
2000
white Ka8 Rd6f5 Sb7
black Ba6c3 Kd3 Qd5 Pa4c6c5f4e5d7e7 Sc4d4
Pb 6 : give all the moves of each solution (reminder, in helpmate, it is Black to start and help White to checkmate ... isn't that nice? ... Ebony and Ivory ... )