[paipa]

I get the dillemma, but I don't think it's a problem that the string of squares used to define "foward" isn't always the same as path the pawn will actually take if it chugs along.

This only happens when there's no straight path to the opponent's backrank, so you are allowed to go "sideways-foward" until you hit a square from which there is a clean forward path again.

Agreed that the past should not matter, only the current position.

[frading]

Thanks a lot for insisting of this, and that end up convincing me. I describe the change in the sibling comment: https://news.ycombinator.com/item?id=40634675

That was super useful. So don't hesitate if you have any other feedback.