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* <strong>Fred Gifford</strong> // [http://www.philosophy.msu.edu/people/faculty/fred-gifford/ website], [http://philpapers.org/profile/45001 PhilPapers]
* <strong>Robert T. Pennock</strong> // [https://www.msu.edu/~pennock5/ website], [http://philpapers.org/s/robert%20pennock PhilPapers]