I have to build a fitch proof for the negation introduction rule
with some constraints: I cannot use ¬¬E, ¬I, RAA (Reductio ad absurdum) and ¬¬I. There is also another constraint saying that I have to use the law of excluded middle (LEM).
There are two tips provided to solve the problem. First of all, I have to use ¬E (or 0I). Second of all, I have to use the disjunction elimination:
The only way I found how to solve it is the following way:
Does anyone have an idea on how to use the disjunction elimination? As my solution doesn't use it?
EDIT 1: Correction in proof
EDIT 2: Thank you so much to @MauroALLEGRANZA for the help. This is what I came up with.
EDIT 3: Here are the rules I can use: https://drive.google.com/file/d/19WQOPuxyskq2s_eWXvR04sl6qMUG5CKx/view?usp=sharing