How can we use double-negation deduction rule? For example, ~~p is the same as p.
I am not able to find how to eliminate ~~ in https://proofs.openlogicproject.org/
Note that they have DNE in their sidebar:
So, click CREATE PROBLEM, put ~~A on line 1 and A for the conclusion. Then click NEW LINE, put A in the first box, then put "DNE, 1" in the box to the right. Click CHECK PROOF.
Now, this may provide the answer to your question, and the Philosophy SE might be about analyzing arguments logically and all, but your issue seems to be a software consideration, not a philosophical one, so please don't accept my answer even if it's sufficient, I don't think I've earned the points for that. (Moreover, then, the OP question is liable to be closed/deleted anyway, so it wouldn't do me any good to get the points, aye?)