# Thread: Mathematical Logic by Cori and Lascar : Possible typo?

1. ## Mathematical Logic by Cori and Lascar : Possible typo?

I have a question on the textbook "Mathematical Logic: Propositional calculus, Boolean Algebras, predicate calculus" by Rene Cori and Daniel Lascar.

On Lemma 1.6 on this page there is a part that says,
"...if $\mathcal{Y}(W)$ and $\mathcal{Y}(V)$ are true, then $\mathcal{Y}(\neg F)$, $\mathcal{Y}(F \wedge G)$, $\mathcal{Y}(F \vee G)$, $\mathcal{Y}(F \Rightarrow G)$, $\mathcal{Y}(F \Leftrightarrow G)$ are also true.".

I think there is a typo there and it should be,
"...if $\mathcal{Y}(W)$ and $\mathcal{Y}(V)$ are true, then $\mathcal{Y}(\neg W)$, $\mathcal{Y}((W \wedge V))$, $\mathcal{Y}((W \vee V))$, $\mathcal{Y}((W \Rightarrow V))$, $\mathcal{Y}((W \Leftrightarrow V))$ are also true.",
WITH THE ADDITION OF THE EXTRA PARENTHESES.

I tried to attach a picture from the next page of the rest of the proof, because that might help, and the google books omits that page. But it doesn't upload. I don't know why. Size is 33kB.

Is this a typo is there something I don't understand?

2. Delete post.

3. I uploaded the rest of the proof to photobucket. It's here.

4. Is this a typo is there something I don't understand?
I think you are right on both counts: it should use W and V and add parentheses.

5. Thanks. I could not overlook the possibility that I might be wrong.

6. The book stipulates the convention that outer parentheses on formulas may be dropped to stand for the actual formula with outer parenetheses.

7. Originally Posted by MoeBlee
The book stipulates the convention that outer parentheses on formulas may be dropped to stand for the actual formula with outer parenetheses.
That's in page 10, right. Thanks. I forgot that.