Seven Languages in Seven Weeks - Prolog Day 1 Self-Study

For this book's section about prolog, I'll be using SWI-Prolog, as I'm currently getting an error installing the gnu-prolog macport. Here's the link to the SWI-Prolog online reference.

Make a simple knowledge base. Represent some of your favorite books and authors.

% books.pl
book(sevenLanguagesInSevenWeeks).
book(cleanCode).
book(cleanCoder).
book(programmingInScala).
author(odersky).
author(tate).
author(martin).
wrote(odersky, programmingInScala).
wrote(tate, sevenLanguagesInSevenWeeks).
wrote(martin, cleanCode).
wrote(martin, cleanCoder).

Find all books in your knowledge base written by one author.

?- ['books'].
% books compiled 0.00 sec, 13 clauses
true.

?- wrote(martin, X).
X = cleanCode ;
X = cleanCoder.

Make a knowledge base representing musicians and instruments. Also represent musicians and their genre of music.

% music.pl
instrument(flea, bass).
instrument(hendrix, guitar).
instrument(hancock, piano).
instrument(cash, guitar).
genre(flea, funk).
genre(hendrix, blues).
genre(hancock, jazz).
genre(cash, country).

Find all musicians who play the guitar.

?- ['music'].
% music compiled 0.00 sec, 10 clauses
true.

?- instrument(X, guitar).
X = hendrix ;
X = cash.