April 2012
Intermediate to advanced
416 pages
10h 40m
English
1. Let us first define: The set of propositional formulae of, say, set theory, denoted here by Prop, is the smallest set such that
(1) Every Boolean variable is in Prop (cf. 1.1.1.26)
(2) If
and
are in Prop, then so are (¬
) and (
) —where I used
as an abbreviation of any member of {⋀, ⋁, →, ≡}.
If we call WFF the set of all formulae of set theory as defined in 1.1.1.3, then show that WFF = Prop.
Hint. This involves two structural inductions, one each over WFF and Prop.
2. Prove the general case of proof by cases (cf. 1.1.1.48):
→
,
→
⊢ ⋁ → ⋁ .
3. Let us prove ...
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