Is there a position where White must play on one of the border rows – 1 or 24 – to guarantee a win (excepting the final two plays, of course) ?

If so, are these positions always of the sort that White plays on row 1 making a link with a peg on row 3? Or is there a position where White must play on row 1 to guarantee a win AND that play does not make any new links?

It’s probably a minor but easy improvement to the bot algorithm if I can ignore those rows until the end.

the third posibility… linking to row 2 surely must happen as well

There are both positions possible, forced links and single pegs on 1st and 24th row although it happens rarely, probably because usually games aren't played out and one player resigns earlier (before that close to the border). It may be possible to make an improvement and only consider moves on 1st and 24th row after the 20th move.

A forced border row peg which links can definitely happen in an actual game:

!http://cf.geekdo-images.com/images/pic1386428.png!

I can show you positions where a non-linking border row peg would be the *fastest* and simplest win, but it would not be the only win.

Hjallti, a move which places a first row peg and links to a second row peg (call this second row peg peg B) is unlikely to ever be a forced move, because the opponent can never block such a move. UNLESS that link were superfluous, and the first row peg threatens to link elsewhere to win. But that would have to be a double threat which excludes that second row peg, and I do not think such a position is possible. If that second row peg B did have a threat, then one could just execute that threat and link to the first row at a later time.

IMO this is a minor issue for a Twixt engine, and you could probably ignore border row moves without significantly affecting performance.

Uh, okay, in the above diagram if there were an orange peg on S23, then the forced move at Q24 would also link to S23 as well as linking to P22. But as I said, this link to S23 is superfluous. And I challenge anyone to describe a position where a non-linking border move is the only way to win. Maybe I gave up too easily and there is a solution.

How about this?

!http://www.popcorn.cc/~zandor/bilder/edge.jpg (board)!

sorry, I mean this:

!http://www.popcorn.cc/~zandor/bilder/edge.jpg!

I hope it works now.

That looks pretty good to me.

Very nice.

This is an example where White's next move must be at K24, right? And if White moves anywhere else, Black can prevent the connection of White's existing pegs to the south?

So, the answers to TwixtBot's first two questions are Yes and No, respectively.

David you need some practice ;-) The answers are no and yes, it's actually all in my first post… Zandor posted the kind of pattern I had in mind, it looks a little bit constructed, but I know I encountered similar positions in real games. Under no circumstances I would completely ignore those moves, because then it is possible to trap the bot.

Btw forced links to 2nd row are also possible. Just add a white peg on M23 in Zandor's position.

I should have written Yes, No and Yes, for the OP's original 3 questions.