Are we allowed to use DeMorgan as a valid inference step?
I have an identity which would suite me changing with DeMorgans law, but I dont know if I am allowed to use "DeMorgan" as a reason, or if I have to put the whole DeMorgan proof in (This would be crap because it would increase the size of the proof by 5 times.)
Ye but the thing is, DeMorgans laws can be proved with the laws of natural deduction. Its just that including that sub proof will increase the size of my proof by a lot :'<
First do the proof for DeMorgan seperately (as the text book did for MT), and then you can refer to it. I think they will burn you for just using DeMorgan without 1st proving it.