Prolog

Prolog (Programming in Logic) is a programming language based on Predicate Logic. It uses the restricted syntax of Horn Clauses:

Predicates, e.g.,	floats(), etc.
Operators	<=, and, not
Logical variables	X, GP, etc.
Constants	7, girl, etc.
Function names	f, left(), ...
Facts	female(girl).
rules	burns(X) <= wooden(X).
queries	? witch(girl).

Quantification of logical variables is implicit -- universal for facts and rules, existential for queries.

The introduction will get you going and there are more examples. The interpreter shows how Prolog works.

<= (also :- ) can be read as if, or as is implied by. planet(P)<=orbits(P,sun) can be read as ∀ P, P is a planet if P orbits the sun. (That is not to say that the definition cannot be tightened.) ?satellite(S) can be read as does there exist an S such that S is a satellite? And the answer, here, is yes, if S is earth's moon, or a moon of another planet.

<= (also :- )	can be read as if, or as is implied by.
planet(P)<=orbits(P,sun)	can be read as ∀ P, P is a planet if P orbits the sun. (That is not to say that the definition cannot be tightened.)
?satellite(S)	can be read as does there exist an S such that S is a satellite?
And the answer, here, is yes, if S is earth's moon, or a moon of another planet.