Logic / Unit 5 Logic 219 short lesson, about 20 seconds
Proving Tautologies
Captions available
The idea
Tautologies are provable from zero premises — open immediately with a CP or IP assumption.
In practice
To prove p ∨ ~p: assume its negation, De Morgan it into p-and-not-p territory, explode, discharge.
Where people slip
A proof with no premises looks impossible for exactly one video's worth of time.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Unlocks
- Nothing yet depends on this.
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