Prolog Tutorial

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A Prolog Compendium (pdf) by Marc Bezem.
This is an excellent conceptual overview of Prolog suitable for the logic programming component of a Principles of Programming Languages course.

Comparison of Prolog implementations: https://en.wikipedia.org/wiki/Comparison_of_Prolog_implementations

Anne Ogborn, Real World Programming in SWI-Prolog: http://www.pathwayslms.com/swipltuts/index.html

"PrologResources", http://www.whoishostingthis.com/resources/prolog/