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


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:

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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):

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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
    Oct 5 '19 at 18:44

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