Talk:Frege's propositional calculus

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== Unicodify?

Is space a critical issue on Wikipedia? The last edit brags of the space saved by Unicodify. But is now harder to edit on many browsers... Nahaj 01:50, 27 January 2006 (UTC)

[edit] Third axiom unnecessary

The article lists the following three axioms of implication:

THEN-1: A → (B → A)
THEN-2: (A → (B → C)) → ((A → B) → (A → C))
THEN-3: (A → (B → C)) → (B → (A → C))

It seems to me that THEN-3 follows from THEN-1 and THEN-2. This is because the first two are enough to prove the deduction theorem. Therefore, in order to prove THEN-3, it is enough to show A → (B → C) ├ B → (A → C). Using the deduction theorem again, it is in turn enough to show A → (B → C), B ├ (A → C), and in turn, A → (B → C), B, A ├ C, which is obvious.

Can anybody confirm that THEN-3 was part of Frege's original axiom system? 136.152.196.167 (talk) 02:27, 3 March 2008 (UTC)