GlossaryThe "Last move(s)?" stipulation is quite explicit. Still, it deserves an entry into the retro-glossary because of the associated concepts.
A "Last Move" problem is especially interesting if
We count retro-moves in single moves, i.e. moves by one side, so that 1. e4 e5 2. Nf3 Nc6 3. Bb5 is 5 single moves. (The "half-move" terminology has other meanings).
We say a (single retro-) move is completely determined if we know the exact from- and to- squares and which enemy unit was captured (if any). That is, when we know exactly how the board was before this last move. Usually, problems asking for "last n singles moves" ask for completely determined moves.
A recent record-breaking problem by P. Wassong and G. Wilts has 55 last single moves completely determined !
Pascal Wassong (version by Gerd Wilts)
Dedicated to Babette
14+12. Last 55 single moves?
Obviously, the choice of potentially possible last moves is larger in Type A problems than in Type B, and in Type B than in Type C. That is why Type A problems are usually preferred.
Here is an example that everybody has already seen. It is a Type B with only one precisely determined last move (reader's exercise: why not the last two single moves?)
3+1. What did White just play?
As an example, here is the (so far) most economical presentation of KxN in Type A (to compare with the problem we just saw and which happens to be the most economical KxN in Type B.)
Hugo August, Otto Brennert,
Thomas R. Dawson, Niels H°eg and
4+3. Last move?