That tutorial is fast, but it's a pretty bad tutorial that will teach you terrible habits and a very incomplete understanding of Prolog. Unfortunately there are

That tutorial is fast, but it's a pretty bad tutorial that will teach you terrible habits and a very incomplete understanding of Prolog. Unfortunately there are no good free ones. Many people seem to like https://www.metalevel.at/prolog https://www.metalevel.at/prolog (featured here several times). Although I don't think it's very good from a didactic point of view, many disagree, and at least the author really knows what they are talking about. I have a PDF of the fifth edition of "Programming in Prolog" by Clocksin and Mellish lying around here. I could swear it was available for free as open access for a while, though a very quick web search doesn't confirm this.