Glossary
Retro-rebuses are problems where you have to decipher an encoded chess position, with legality as a constraint.
This kind of problems was invented by Frolkin in the 70's. It is a generalization of (and includes) the earlier coloring problems.
Here is the earliest example :
A. Frolkin and A. Kornilov Rex Multiplex 6, Apr. 1983
17. Associate a different chess unit to each letter. (b) Ag1 -> b1
Here C and E are the only non-adjacent single-occurrence letters, hence they must be the 2 Kings. Now B must be a wh.P because any other unit would give illegal checks to one of the Kings.
The rest is decoded in the same way. (See full solution if you can't work it out yourself.)
