Cita APA

Helly, W., & Helly, W. (1975). Urban systems modelds. New York, New York: Academic.

Citación estilo Chicago

Helly, Walter, y Walter Helly. Urban Systems Modelds. New York, New York: Academic, 1975.

Cita MLA

Helly, Walter, y Walter Helly. Urban Systems Modelds. New York, New York: Academic, 1975.