Recently, two people emailed me asking the same question about my puzzle collection: they wanted to know how it's possible for Mines, my Minesweeper implementation, to guarantee that every grid can be solved without guesswork.

So I wrote up a longish answer to that question, and sent it to both people. And it seems like a waste not to post it here too. Perhaps it could be article number 2 in the informal series that also includes the article I wrote in March about how the solver for Net works.