Harper, D. (1989). Logo: Theory & practice. Brooks/Cole.
Cita Chicago (17th ed.)Harper, Dennis. Logo: Theory & Practice. Pacific Grove, Calif: Brooks/Cole, 1989.
Cita MLA (9th ed.)Harper, Dennis. Logo: Theory & Practice. Brooks/Cole, 1989.
Atenció: Aquestes cites poden no estar 100% correctes.