Last Move?-Records: New Definition and new Types

One of the best known retro-themes is the economy record for the 'What was the last move?' stipulation, i.e. the most economic representation of a uniquely determinable last move. The following economy criteria are used:

1) The fewest number of pieces (K, Q, R, B, S, P)
2) The fewest number of officers (K, Q, R, B, S)
3) The fewest number of 'heavy' officers (Q, R)
4) The fewest number of queens.

60 Different move types (records) exist:

- K, Q, R, B, S, P move (6 move types)
- K, Q, R, B, S, P captures Q, R, B, S, P (30)
- P moves and promotes to Q, R, B, S (4)
- P captures Q, R, B, S and promotes to Q, R, B, S (16)
- P makes a double move (1)
- P captures en passant (1)
- Castling (2)

Furthermore, there are different types:

Type A: No indication as to who has the move, no king is in check (59 different move types, no e.p.)

Type B: Who has the move is indicated, no king is in check (59 different move types, no e.p.)

Type C: A king is in check (60 different move types)

This definition of Type C is new! The current definition is: "No indication as to who has the move, a king may be in check". As a consequence, a Type A record could also be a Type C record. This has always been criticised by retro-friends, and on Internet one can find different definitions. Therefore I proposed the new definition, which clearly differentiates Type A (without check) and Type C (with check), and which offers more record possibilities (especially in the fairy field). The new definition was approved by M. Caillaud, W. Dittmann, A Frolkin, H. Gruber, A. Kornilov, G. Lauinger, N. Plaksin, M. Richter and B. Schwarzkopf, and is effective with this publication.

In orthodox chess, the new definition affects only two out of the 178 A/B/C records: The records for KxQ and PxQ=S. Of course #1 (13 pieces) is still the record for KxQ in Type A (and Type B). The "new" record for Type C is #2 (14 pieces), originally intended for the related theme "What is the mating move?". It is more economic than the elder problem by L. Borodatov (Die Schwalbe 1984, Ka7 Ba5 Be8 Pb4 - Kd8 Ba8 Bb7 Bc8 Pa6 Pb5 Pc6 Pd7 Pe7 Pg7, Last move?). Similarly, #3 (12 pieces) is still the record for PxQ=S in Type A (and Type B). The "new" record for Type C is #4, which also has 12 pieces but one officer more.

[The rest of the article is about Duplex Last move and Equal last move]

1 - Luigi Ceriani

problem 1951

1st Prize

2+11. Last move? (record for KxQ Type A)

[3bkN1K/pppprp1p/4p1p1/8/8/8/8/8]

2 - Werner Keym

Die Schwalbe 1990

3+11. Last move? (record for KxQ Type C)

[n1k2Rn1/BppppKp1/1p3p1p/8/8/8/8/8]

3 - V. Bartolovic, Z. Maslar

problem 1957

6th Comm.

Last move? (record for PxQ=S Type A)

[2bK1kN1/1pppprp1/5p1p/8/8/8/8/8]

4 - Leonid Borodatow

Die Schwalbe, 1980

3+9. Last move? (record for PxQ=S Type C)

[rN3b2/pp1pp1p1/k1p5/P1K5/8/8/8/8]