Reading a logical statement precisely

Contest logic turns on small words. All, some, none, only, at least and exactly mean different things, and the opposite of all are red is not none are red but at least one is not red. Reading the sentence twice is a mathematical step.

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Work through it

LearnWhat it is, how to spot it, a worked example, and where it goes wrong.
Practice — 3-point ladder1 problem. Three in a row finishes it.0/3 in a row · 0/1 solved
Practice — 4-point ladder4 problems. Three in a row finishes it.0/3 in a row · 0/4 solved
Practice — 5-point ladder1 problem. Three in a row finishes it.0/3 in a row · 0/1 solved
Skill quizFinish every ladder that has problems first.Finish the ladders above first

Before and after

Needs first

Nothing. This is one of the skills the Atlas starts from.

Opens up

LOG-02Truth-tellers and liars LOG-03Elimination grids LOG-05Parity arguments LOG-08Working backwards LOG-09Informal proof by contradiction

In official papers

No indexed official paper question has been tagged with LOG-01 yet. The index grows one paper at a time, and it records only question numbers, point values and our own skill tags — never the problems themselves.

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