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2016-01-27 02:42:02 Post No. 7813432
Post No. 7813432
>tfw can't do Hilbert style proofs in propositional logic
Kill me now.
Can someone give me some tips? How do I "see" what sort of wffs to plug into the schema when doing a proof? Here's an example (> for if..then):
Prove that A > A
1. A > ((A > A) > A) /// instance of H1
2. (A > ((A > A) > A)) > ((A > (A > A)) > (A > A)) /// instance of H2
I'm not gonna type the rest of the proof, but you get the idea. How do I figure out that I need to substitute (A > A) for B? Whenever the texts show the proof in full, I can follow it no problem, I just cannot fathom how I'm supposed to figure out what to substitute into the schema.
Should I even bother learning axiomatic proofs when natural deduction exists?