This is a tree of proof, also called search tree. It helps understanding how solutions are found for your querys. You can read more about it here.
These can been viewed for each step by hovering the mouse over an edge for a few seconds.
Zoom: mouse wheel; Moving around: drag nodes or drag on free space
You may try and right click on the tree. Firefox and Chrome both offer an option to save it as an image file.
This is a very limited subset of Prolog! Don't get fooled by the syntax highlighting; it might provide highlighting for features that are not actually supported, because we didn't write the editor specifically for this interpreter.
These are the limitations:
The Prolog subset understood by the program can be viewed as a grammar here.
It is one of the few, if not the only Prolog interpreters that does a breadth-first-search as its SLD resolution strategy. This strategy/algorithm is semidecidable as opposed to the more common (and more efficient) depth-first-search, which is neither decidable nor semidecidable.
In simpler words: you are less likely to run into infinte loops. Consider this example:
a(X) :- a(X). a(a). ?- a(Z).
That program and query will run infinitely on a normal Prolog interpreter while this one will give you all solutions.
The project was started in summer 2019 by Leonhard Kipp who coded the actual interpreter backend. Martin Weber joined the project later to create this web front end. Both are students of computer science at FH Aachen University of Applied Sciences in Aachen, Germany.
Yes. The project is hosted on Github.