Deduction

DEDUCTION

Deduction — Daily deduction puzzle

A free daily logic grid puzzle. Light or darken every window using clues that are all true - solvable by pure elimination, one answer, no guessing. No account.

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Mekemad er a game

Kuk a melekoi Deduction

Deduction is a daily logic grid puzzle. The board is a grid of windows - 5 across and 4 down on the daily - and every window finishes either lit or dark. Nothing starts filled in; what you get is a list of about twelve clues, all of them true and all of them visible from the start. They talk about counts along a row or column, about a window’s eight neighbours, about two windows matching or differing, and about what lies further along a line. Together they leave exactly one possible grid, and that grid is always reachable by elimination alone - both properties are proven by separate checks before the board is served, so you never have to guess. Tap a window to light it, again to darken it, a third time to leave it undecided. A clue greys out once it has nothing left to teach you. Free, no account, and the same board worldwide.

How Deduction works

Deduction is a logic grid puzzle - the family that contains the zebra puzzle and Einstein’s riddle. The board is a grid of windows, 5 across and 4 down on the daily, and each one finishes either lit or dark. Nothing is filled in when you start.

What you are given instead is the clue list beside the board. Every clue is true, and every clue is visible from the first second - there is no progressive reveal. A clue talks about counts ("row 3 has exactly 2 lit windows"), about neighbours, about one window relative to another, or about what lies along a row or column in a given direction.

Those clues together pin down exactly one grid. That is proven twice before a board is served, by two checks that share no code: one walks the clues one at a time to confirm the answer is reachable by elimination alone, the other searches the whole space to confirm no second grid fits. So you never have to guess and back out - there is always a window somewhere that one clue on its own decides.

Input is a three-state tap: undecided, lit, dark, undecided again. A clue greys out the moment no possible completion of the grid could break it, which is the puzzle telling you it has nothing left to give. A clue turns red when the grid already contradicts it.

The daily board is the same for every player in the world. A daily clue carries nothing but whole numbers and grid coordinates - no names, no objects - so it survives translation into every language we ship without the puzzle changing. Your solve time goes to the global leaderboard, and Deduction Unlimited generates fresh boards on demand without touching your streak.

Omekerull me omengereomel

1
The anchor clue is always there

Exactly one clue states a single window’s state outright, and every puzzle has one. If you are staring at a blank grid wondering where to begin, that is where.

2
Count what is owed, not what is placed

Walk each counting clue asking how many lit windows it still owes. A clue owing zero decides every remaining window in its set as dark; a clue owing as many as it has undecided windows decides them all as lit.

3
Comparison clues bound both lines at once

"Row 1 has more lit windows than row 4" is worth more than it looks: it means row 4 cannot be full and row 1 cannot be empty, before you know a single window in either.

4
A dimmed clue is a finished clue

Greyed clues cannot help you again. When you are stuck, reading only the black ones typically cuts the list you are scanning in half.

5
Pin the two or three you keep returning to

Tapping a clue pins it to the top of the list. On a twelve-clue board the two clues that interact with the region you are working on are worth keeping in view.

6
Back out of a contradiction, do not patch it

When a clue flags red, the contradiction is a fact about the grid, not about the window you just tapped. The real mistake is usually two or three decisions earlier - undo rather than building on it.

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What is Deduction?
Deduction is a daily logic puzzle on a small grid of windows. Every window ends up either lit or dark. Beside the board is a short list of clues - all of them true - and together they leave exactly one possible grid. The daily board is 5 windows wide and 4 tall, twenty windows in all, with around twelve clues.
Do I ever have to guess?
No, and that is checked rather than promised. Before a board is served it is run through two separate proofs: one confirms the answer is reachable by applying one clue at a time to the partial grid, the other confirms no second grid satisfies every clue. A board that needs trial and error is thrown away and a new one generated.
Why do some clues go grey?
A clue dims once no possible completion of the undecided windows could break it - at that point it cannot teach you anything new. It stays on the list, because it is still part of the puzzle; it just steps out of the way. Tap any clue to pin it to the top of the list.
What counts as a neighbour?
All eight surrounding windows, diagonals included. The direction words - left, right, above, below - work differently: they always mean along the same row or the same column, never diagonally, and they never wrap round the edge of the board.
Is the puzzle the same in every language?
Yes. The daily board is identical worldwide and only the clue sentences translate. That is possible because a daily clue carries nothing but whole numbers and grid coordinates - there are no names or objects in it to inflect - so the same puzzle reads correctly in every language we ship. Stats and the leaderboard are consolidated globally rather than split per language.
Is unlimited proved the same way as the daily?
Yes - unlimited calls the same generator, so every practice board is proved unique and reachable by elimination before it is served. What changes is the bookkeeping: unlimited draws a fresh board on demand, never hands you today's daily, and leaves your streak and the leaderboard untouched.

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