How can I set up en passant in the Popeye engine?

Question

I want to solve a problem with Thomas Maeder's excellent Popeye engine, and to specify that a possible en passant in the diagram is ok. How can I do this please? The documentation seems opaque. Thanks so much!

See https://github.com/thomas-maeder/popeye/releases/tag/v4.81

EDIT: Outside chess, I see stackexchange used widely to ask technical questions about software use (indeed use it myself like this sometimes), and I think this is fair use in chess too.

Answer 1

The github page lists several help files in various languages: English, French and German. These are text files which can be downloaded. English is clearly not Thomas Maeder's mother tongue, I'm guessing German. Perhaps the German help file is clearer than the English.

As far as I can tell from the English file there is a long list of options you can pass to the program to define the problem you want it to solve. For en passant it defines the "EnPassant" option as follows:

EnPassant - Must be followed by 3-4 squares which indicate the pawn move just played:

• departure square
• avoided squares
• arrival square

Answer 2

Thanks, inspired by Brian's response, I have tried the following input:

begi 
prot outputp.txt 
piec White Kf5 Qf8 Ph5 Black Kh7 Pg5 
stip #1
opti enpa g7g6g5S 
next 
piec White Kf5 Pg4 Rf6 Black Kh4 Pf4 
stip h#1
opti enpa g2g3g4
end

which successfully gives the following outputs:

1.h5*g6 ep. #
1.f4*g3 ep. Rf6-h6 #

So I think that's it. Thanks again.