7

The PGN "Standard" (if you want to call it that, because it is very flawed and seems out of date), states:

  • First, if the moving pieces can be distinguished by their originating files, the originating file letter of the moving piece is inserted immediately after the moving piece letter.
  • Second (when the first step fails), if the moving pieces can be distinguished by their originating ranks, the originating rank digit of the moving piece is inserted immediately after the moving piece letter.
  • Third (when both the first and the second steps fail), the two character square coordinate of the originating square of the moving piece is inserted immediately after the moving piece letter.

What I want to know is this: what situation could give rise to the third case?

As I think this through, I cannot for the life of me think up a scenario that the first or second disambiguation rules wouldn't comprehensively cover.

8

Yes, it's possible for a piece to need both the rank and file to distinguish it, although it's rare. For example:

[FEN "8/1k6/8/8/5Q2/8/3Q1QK1/8 w - - 0 1"]

1.Qf2e3
3
  • Incidentally, I once made a chess problem stipulating to play the fastest game leading to such a situation; try to find it! Dec 25 '20 at 9:17
  • @HaukeReddmann I'm sure this is not it, but the fastest one I find is 11 moves, White's moves being 1. e4 2. exd5 3. Nc3 4. d6 5. dxe7 6. exf8N 7. Ne6 8. Ng5 9. Nge2 10. Ng3 11. Ng3e4.
    – bof
    Dec 25 '20 at 11:02
  • Thanks for the quick answer. Clear and unambiguous! Dec 25 '20 at 14:21
7

@DM showed one possibility, which would also work with bishops (and on various other places on the board, with the three pieces at corners of a square). The only other option is with knights:

[FEN "8/1k6/8/8/5N2/8/1N3NK1/8 w - - 0 1"]

1. Nf2d3
3
  • 3
    The example with knights is best, only one promotion needed.
    – bof
    Dec 25 '20 at 11:20
  • Why are knights "the only other option?" Surely it can occur with rooks... Jan 4 at 3:46
  • @BrianMcCutchon no, you need some kind of diagonal movement for this kind of ambiguity.
    – Glorfindel
    Jan 4 at 7:02

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