L.Ceriani:  White retracts and then #1. A plausible try: Nd6xBc8 retracted Back

In order to understand this puzzle by Ceriani you need to know something about the Mutachromatic chess. As you may know the Monochromatic chess is a variant of chess, where all pieces always move on same colored squares. Mutachromatic chess (mutachess) is in fact just an opposite. Here are some definitions: Mutachromatic chess  = A piece always moves to the square of opposite color. Naturally Mutachromatic Position (NMP) = A position that has been reached from the initial position by mutamoves and cannot be achieved by any other way. A position can be identified as a NMP, if it has following features: - All bishops are on their initial squares. - All pawns are on their initial squares - except rook pawns may  have taken a single step forward. (Not a double step) - No other pieces than queens may have been captured. Mutachromatic pieces = Kings,Rooks,Knights and rookpawns, while in NMP. Now that we know the basics of mutachess, we are ready for an interesting aspect of NMP. There is namely a very simple rule to check who is to move in any NMP: If the number of mutachromatic pieces on white (black) squares is - Odd, it is white-to-move next. - Even, it is black-to-move next. The lower diagram on the left present the position after white has retracted a plausible last move  Nd6xBc8 and black has retracted the capture a7xNb6. Armed with the knowledge above, we now recognize this position as NMP. Therefore it is possible to say who is to move next. Counting the mutapieces on white:Rb1+Kd1+Rh1+Ph3+Rh7+Ne8+Na8=7 ,which is an odd number and therefore it is white to move! But we just retracted a black move a7xNb6. However,  the position with black to move is illegal (Try to achieve this from initial position) and therefore the retraction of Nd6xBc8 is not correct. Luckily there is an alternative of Nd6xQc8, which is correct. After this and further a7xNb6 retraction the position is not NMP any more and black can easily lose a tempo if needed before an earlier NxBc8 is retracted rendering the position NMP.