The knowledge base called
contains a number of facts about
European countries, capitals, rivers and seas. You can view it
showlib countries.pl from Prolog.
I hope the meaning is clear. In the facts for
has_capital, the first name is always that of a country, the second of
a town (or city). In those for
is_on, the first name is a town, and
the second is either a river or a sea.
linked_to is about rivers and seas: there is one fact for each
river that flows into another river or a sea.
next_to tells you which
seas (not rivers) are next to one another.
borders is like
next_to, but is about countries, not seas. It
tells you which countries share a common border.
on_sea tells you which countries adjoin a given sea.