How to identify invalid proposition

Question

In propositional logic, how do i identify if a [compound/non-compound] proposition is valid or not? do the parenthesis matter, even if they start and do not end etc...? for example:

(P (and (not Q)))) or R))

or what about: ((P and Q) or R

Answer 1

Strings such as your examples where the parentheses do not match are not well-formed at all, and so asking whether they are valid is not even a meaningful question. Logical validity is a property that applies to well-formed formulas, not to arbitrary strings.