Analysis board FEN sometimes incorrect

I use Firefox on Ubuntu.

After playing the move 1. e4 on the analysis board, the FEN field contains: "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq - 0 1". To the best of my understanding, this should contain "e3" not "-" to indicate the En-Passant square, as follows: "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1".

Does this happen for other people too?

Anyway best of luck to Lichess getting v2 up and running - great work so far!

sethbae

It may be considering only possible en-passant moves, I suppose.

Since the information about en passant is redundant when en passant is not possible, it logically follows that the simplified form is more standard. Consider three-fold repetition for example. On the other hand, omitting the redundant information will never cause any bugs in any program or engine that plays standard chess. Of course in some custom variant this information could become useful.

I thought it might be only shown if relevant (i.e. if EP captures can be made), but Wikipedia actually gives this position as an explicit example (en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation), with e3 and not a dash.

Both forms are in use.

Do you have any evidence to support that if you could be so kind?

The FEN standard does require the en passant target square even if there is no legal en passant move. However, for 3fold repetition reasons the en passant square is only relevant if there is a legal en passant move.

So the FEN standard is a constant cause of confusion and bugs for chess software developers and nobody follows it.

But in order to claim threefold repetition, I think the position needs to have occurred 3 times with the same EP rights, doesn't it? To me it still seems unlikely that Lichess are purposefully displaying an incorrect or non-standard FEN.