Last Move?

Glossary

The "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

many last moves are completely determined, or
the last move is tricky, or
the problem is economical, or
all of the above.

Precise single retro-moves

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

[7B/b1pp2p1/N1p1p3/2K5/PP6/1Pk1Pp2/QRPNrP2/nRqrB3]

14+12. Last 55 single moves?

Type A, B & C

There is a classification of "Last Move" problems:

Type A: It is not given who has the move. Neither king is in check.
Type B: The stipulation says who has the move. Neither king is in check.
Type C: It is not given who has the move. A King is in check.
Type D = duplex Type B: One solution assuming White has the move, another one solution assuming Black has the move (not covered here)

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?)

J. Mortensen
1956

3+1. What did White just play?

Economy records

These records attempt to present a given retro-move (e.g. O-O, or PxB=Q) in a "Last Move" stipulation using as few men as possible.

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 Høeg and Valerian Onitiu
Skakbladet, 1924

[8888/P7/kP6/prP5/K7]

4+3. Last move?