I can't seem to figure out how to get past this step. Any suggestions? enter image description here


1 Answer 1


If you are able to use modus tollens, then the result would follow quickly. Here is an example of that using a different proof checker:

enter image description here

However, if you have to derive this using introduction and elimination rules, the following might work using a proof provided by the authors of forallx (page 170):

enter image description here

Kevin Klement's JavaScript/PHP Fitch-style natural deduction proof editor and checker http://proofs.openlogicproject.org/

P. D. Magnus, Tim Button with additions by J. Robert Loftis remixed and revised by Aaron Thomas-Bolduc, Richard Zach, forallx Calgary Remix: An Introduction to Formal Logic, Fall 2019. http://forallx.openlogicproject.org/forallxyyc.pdf

  • Thanks so much!! This was very helpful
    – Grace
    Commented Oct 5, 2019 at 18:44

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .