Length records in "Last N single moves?" problems

compiled by Thierry Le Gleuher & Alain Brobecker, march 2007

This page shows retrograde analysis problems where the solver is asked to find the last N single moves played to reach the position.  The design objective is to maximize N and minimize the total number of units, M. Records are positions where one can improve neither of M or N, without worsening the other.

This is an extension of the "Last move" task, discussed in several webpages. Records are classified in the following six categories:

• 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: One king may be in check.
• Type D: Duplex type B.
• Type E: Colouring problem, where no piece attacks both kings.
• Type F: Colouring problem, where a piece may attack both kings.

The number in the first column is M. Then there is one column per problem type, T. The non-blank cells show the records: the cell (M, T) contains the value of N.

When a record also applies to a less restrictive type, then the cell instead contains the letter referring to the least restrictive type.

In some cases, a record for Type C, apart from the last move, can also apply as a record for Type B: this is denoted C or Cx depending on whether the last move was a capture.

The problems here are also available from Alain as a pdf.