Genus Theory - Reversible Moves

Reversible Moves

It is important for further understanding of Genus theory, to know how reversible moves work. Suppose there are two games A and B, where A and B have the same options (moves available), then they are of course, equivalent.

If B has an extra option, say to a game X, then A and B are still equivalent if there is a move from X to A.

That is, B is the same as A in every way, except for an extra move (X), which can be reversed.