I can't seem to figure out how to get past this step. Any suggestions?
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I assume you are not permitted to use or do not have modus tollens. en.wikipedia.org/wiki/Modus_tollens– Frank HubenyOct 3, 2019 at 20:50
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1 Answer
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:
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):
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
answered Oct 3, 2019 at 20:58
