Natural Deductive Logic: DERIVABLE RULES (MT, HS, DS, DeM)

[@user-ke2rp4gz2c]

hi, does anyone know what app he is using for the note taking in this video?

[@Trevtutor]

PDF Annotator for these videos. Windows Journal for the ones older than a year ago.

[@user-ke2rp4gz2c]

@@Trevtutor Thank you for the fast reply!

[@atana.potnia]

I'm not sure I'm quite getting the difference between RAA and Contradiction Introduction.
Edit: My bad, I just noticed rewatching the video that it does say it's RAA but with the symbol.