Truth-tellers and liars

Some speakers always tell the truth and some always lie. The method is to assume one speaker is truthful, follow the consequences all the way, and see whether anything contradicts. If it does, that assumption was wrong, which is itself information.

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LearnWhat it is, how to spot it, a worked example, and where it goes wrong.
Practice — 3-point ladderNo problems written at this tier yet.Nothing written at this tier yet
Practice — 4-point ladder1 problem. Three in a row finishes it.0/3 in a row · 0/1 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

LOG-01Reading a logical statement precisely

Opens up

LOG-09Informal proof by contradiction

In official papers

No indexed official paper question has been tagged with LOG-02 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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