Kytael comments on SotW: Be Specific - Less Wrong

37 Post author: Eliezer_Yudkowsky 03 April 2012 06:11AM

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Comment author: meeple 03 April 2012 03:19:19PM *  0 points [-]

It seems natural to evaluate existential quantifiers using model-checking and any universally quantified statement can be transformed into an existentially quantified statement by applying double-negation and moving the inner negation through the quantifier.

Example:

forall x. p(x)

not (not (forall x. p(x)))

not (exists x. (not p(x)))

But I can't think of how to apply this to Yudkowsky's example so it's probably useless for teaching :P

Comment author: [deleted] 03 April 2012 06:56:06PM 1 point [-]

Here's one way that this could be transformed into an exercise: Have the instructor read a proof (or a fake proof) from, say, formal logic or set theory, and ask the students to follow along step-by-step using a simple example (a la Richard Feynman). Then, at the end of the proof, the students have to explain whether the proof is or is not valid using their example. E.g.:

Instructor: forall x. p(x)

"Ok, let's see, 'all ice cream cones are delicious'."

Instructor: not (not (forall x. p(x)))

"It's not true that 'not all ice cream cones are delicious'."

Instructor: not (exists x. (not p(x)))

"Therefore, 'there is never going to be an ice cream cone that is not delicious'. Valid!"