2250 Lecture : 3.3-5 answers.pdf
5 Feb 2013
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Document Summary
Most answers to the metatheory questions in 3. 3-3. 5 were quite well done, with only minor infelicities in the presentation of generally sound arguments. Two infelicities, both easily repaired, stood out: confusing sentences with sets. This mistake leads to strictly meaningless assertions like set is true or sentence is consistent only sentences can be true or false (on a truth value assignment) or truth-functionally true, false, or indeterminate. Rather than say that a set is true on a truth value assignment (or t-f true, etc. ) you have to say that all the sentences in the set have this property. Similarly, only sets can be t-f consistent or inconsistent. If you want to talk about the sentences contained in t-f consistent sets, you cannot say that they are t-f consistent. You must say that they are true on at least one truth value assignment.
