The Retrograde Analysis Corner
Due to changes in the Codex
of Chess Composition 2009 this article is outdated; but on the
other hand it may still be valid for problems prior to these
changes. See also Castling and
In some situations where a retrograde analysis proves mutual dependency
(or mutual exclusion) between several elements pertaining to legal future
moves, it is sometimes interesting to consider that the position is
in fact a set of twin positions with different histories entailing different
potential futures. They are retro-variants.
In that case, it is customary to insert "(RV)" in
the stipulation. This draws the solver's attention to the fact that
the several different possibilities have to be considered (and solved)
in turn, usually with different solutions.
Here is an example:
The Chess Amateur, 1922
5+3. (RV) Mate in 2
Here if Black still has the right to castle, then his last move was
0 ... g7-g5. Following the RV convention, we consider the two possibilities:
Notice that under the usual convention the problem is not solvable:
White is not allowed to capture en passant
and Black is allowed to castle ! Also, the
RV viewpoint opposes the priority rule for
mutually exclusive castlings.
Such situations led several authors to argue that RV should be the
default viewpoint when mutual dependencies occur. However, the logic
behind it is not perfect. E.g. in the example we just saw, it could
be argued that there is a third possibility: Black can't castle and
the last move was g7-g5. And here both 1. hg6 and 1. Ke6 mate in two.
Clearly this is not the intention of the author.
One sometimes meet (PRA) (for Partial
Retro-Analysis) instead of (RV). This was the earlier
way of stipulating that the retro-variants had to be considered in turn.