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An original game about working out a rule you were never told. A machine is hiding one — something like blue, or not a triangle, or two shapes and a square — and all it will ever tell you is yes or no. You start with two cards it accepts and two it rejects, then you build cards of your own and feed them in one at a time. This is not guessing a hidden code; it is guessing a hidden idea, and the difference is that a single well-chosen card can rule out half the possibilities at once.
Every card has three things about it: a colour, a shape, and how many shapes there are. Three choices each, so twenty-seven cards exist in total. The hidden rule is always about those three things — a single value like green, a negation like not a circle, or two values joined by and or by or.
The green column holds cards the machine accepts and the red column holds cards it rejects. Two of each are given to you for free. Pick a colour, a shape and a count from the three rows, then press Test to see which column your card lands in. Testing costs nothing but time, and the clock never stops.
When you think you have it, press I know it. Four fresh cards appear and you mark each one as following the rule or not. Get all four right and the rule is yours; the next one will be drawn from a slightly wider set of possible rules. Get any of them wrong and the rule is revealed and a new one begins.
Those four cards are picked so that any two rules still consistent with your evidence would answer them differently, so guessing your way through almost never works. Narrow it down properly and you cannot fail.
The run lasts three minutes and your score is the number of rules found.
The instinct everyone has at the start is to test a card they expect the machine to accept. That is the weakest move available. A card you are confident about teaches you almost nothing, because you already knew the answer. The card worth playing is the one you genuinely cannot predict, because whichever way it lands, half of what you were considering dies.
Change one thing at a time. If a green square pair is accepted, do not jump to a red circle triple; try a red square pair. Now the answer tells you about colour alone, with nothing else muddying it. Sweeping changes give you an answer you cannot attribute to anything.
Watch the rejected column as closely as the accepted one. Two rejects that share a property are often more informative than two accepts, because a rule that admits a lot of cards is pinned down faster by what it excludes. When the red column has cards of every colour, colour is probably not the whole story.
Once the rules can contain and and or, the shape of your evidence matters more than its size. An or rule accepts a great many cards, so a long run of accepts should make you suspect one; an and rule rejects nearly everything, so a column of rejects with one lonely accept is the signature. If you find yourself with six accepts and one reject, stop testing cards you expect to pass and go hunting for a second reject.
Finally, remember that pressing the confirm button is free but wrong answers cost you the whole puzzle. If two possible rules are still standing, one more test is almost always cheaper than a coin flip.