This comment breaks the HN guidelines. It is of course fine to ask about licensing, but to use that as a reason to dismiss an entire project is not cool. Nothing that this project does with Python and Prolog gets less interesting because the author hasn't put up some license boilerplate yet. If you wouldn't mind taking the intended spirit of https://news.ycombinator.com/newsguidelines.html more to heart, we'd appreciate it. Note this one: "Please don't post shallow dismissals, especially of other people's work. A good critical comment teaches us something."
Early work, especially early work being discussed in public, is delicate and one should approach it with respect. Otherwise you (I don't mean you personally, but all of us) end up contributing to crushing new shoots of growth and that is not an optimal strategy.
The author is a student and does not seem to be the one who submitted the project to HN. If you need an open source license to the work, you should give the author the benefit of the doubt and request it by opening an issue on the project.
It's really not playing nicely to create a closed frontend to Prolog implementations which are open source, particularly the GPL ones. It seems like they aren't violating the licenses of those Prologs, but just because something isn't against the law doesn't mean it is ethical.
Out of curiosity: if somebody developed this front-end purely to satisfy their own curiosity and never released it, would you consider that to be unethical? If not, how is posting the source code without an explicit license grant worse?
Early work, especially early work being discussed in public, is delicate and one should approach it with respect. Otherwise you (I don't mean you personally, but all of us) end up contributing to crushing new shoots of growth and that is not an optimal strategy.
(A current related thread is https://news.ycombinator.com/item?id=24836090, on pg's recent essay on Early Work.)