The line
Logic grid puzzles.
Match a few people to a few things using a list of clues. You cross out what can't be true and keep going until only one arrangement is left.
What we guarantee
Three promises we can actually check.
Exactly one solution
Every puzzle gets solved exhaustively before it ships. If there's a second arrangement that fits the clues, we throw it out and make another.
No guessing, ever
You can reach the answer by deduction from the first clue to the last. If our solver has to guess and backtrack, so would you, and we don't ship those.
No padding
Every clue in the list is doing work. Take any one of them out and the puzzle stops having a single answer.
How they are made
Generated, then proved.
Lots of puzzle books ship grids with two valid answers, or ones you can only crack by guessing and backing up when it goes wrong. Either way you've stopped solving and started grinding.
So we do it backwards. We generate a puzzle, then have a machine solve it using only the techniques the book has taught you by that point. It ships if it passes all three checks above, and most don't.
Difficulty means more puzzle, not less help
A harder tier means bigger grids, more categories, and more kinds of clue in play. It never means we've held a technique back to slow you down.
The ladder goes Introduction, Easy, Medium, Hard and Expert, then three more tiers for people who want a proper fight.
If you get stuck
There is always another deduction.
That's what the guarantee buys you: when a puzzle stops moving, the next step is there and you already have what you need to find it. Nine times out of ten something got marked wrong twenty minutes back.
Every book has the full answer key in the back. If that's more than you want, tell us how far you've got and we'll give you just the next step.