Delete post.
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 and are true, then , , , , are also true.".
I think there is a typo there and it should be,
"...if and are true, then , , , , 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.
Propositional Formulas are defined in Definition 1.2 on this page.
Is this a typo is there something I don't understand?