Glossary
Due to changes in the Codex of Chess Composition 2009 this article is outdated; but on the other hand it may still be valid for problems prior to these changes.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 En-passant capture.
A Partial Retro-Analysis occurs in positions where it is possible to conclude e.g. that one in a set of possible en-passant captures is legit but we can't tell which one exactly. Or that one in a set of castlings is forbidden, but we can't tell which one.
When "(PRA)" appears in a stipulation, it means that the different possibilities have to be considered in turn (as different problems). In this practical sense, PRA is just another name for Retro-Variants. PRA was the terminology favored by K. Fabel but RV is now the standard. (At least it should be !)