Can you ask questions to find out:
black_sea, and has a capital which is on the
There is another fact in this knowledge base, called
This is defined as follows:
The idea it expresses is that river X flows to river or sea Y if the
water from X flows directly or indirectly to Y. Try the question
and compare it with the results from
Translate the definition into good English (using pronouns instead
of variables). Why do you think it works?
your first example of a technique, very common in
logic programming, called recursion,
where something is defined in
terms of itself. If you have studied grammars in linguistics, or
programmed in high-level languages before, you may have encountered it
already. We shall see several more examples.