Logic / Unit 5 Logic 217 short lesson, about 20 seconds
Indirect Proof
Captions available
The idea
To prove p: assume ~p, derive a contradiction (q · ~q), then discharge — p exits to the main line.
In practice
If denying it explodes, it's true. Video 140's totality, weaponized.
Where people slip
Any explicit contradiction ends the sub-proof — it needn't involve p. The absurdity is the point, not its subject.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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