Re: Answer "how to prove ~(P <--> Q) |- ~P <-->Q "

herbzet <herbzet@xxxxxxxxx> writes:

"Jesse F. Hughes" wrote:

herbzet <herbzet@xxxxxxxxx> writes:

If you enjoy this sort of thing, try

(P -> Q) & (R -> S) |- (P v R) -> (Q v S).

I've been too lazy to work it out Copi style.

Doesn't your copy of Copi have "Constructive Dilemma" (CD)?

I blow the dust off my copy: why yes, it does!

1. (P -> Q) & (R -> S)
2. P v R (Assumption)
3. Q v S 1,2 CD
4. (P v R) -> (Q v S) 2-3 CP

My copy doesn't have CP. What is CP?

Conditional proof (sometimes called -> intro).

Assume P. Derive Q. Conclude P -> Q.

--
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a while, soon be ignored, except for people coming to read my reply,
and your satisfaction will fade as you move on, and I'll still be the
guy." -- James S. Harris will *always* be the guy. Duh.
.

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