I have the following:
$(\neg A \lor B) \rightarrow (\neg A \lor B) \\ (\neg A \lor B) \\ \vdash \neg A \lor B $
And in my mind this seems like a legitimate use of the Modus Ponens rule. But the textbook I'm using disagrees.
Why is this wrong?
The textbook has the following line in it as a part of a larger exercise:
The exercise asks to state whether the use of a giving rule is valid in each case. In the answer section it is marked as an invalid use.