Our book is featured as one of the online Prolog learning resources in the newest publication: Using SWISH to realise interactive web based tutorials for logic based languages, by Jan Wielemaker, et al. In section 3 pages 8 and 9) it names Simply Logical and Lear Prolog Now! as two major online interactive Prolog learning resources!
Using SWISH to realise interactive web based tutorials for logic based languages
Wielemaker, Jan & Riguzzi, Fabrizio & Kowalski, Robert & Sadri, Fariba & Calejo, Miguel (2018)
The full publication text is available here.