Cita APA (7a ed.)

Helpman, E., & Krugman, P. R. (1991). Trade policy and market structure. MIT.

Cita Chicago Style (17a ed.)

Helpman, Elhanan, y Paul R. Krugman. Trade Policy and Market Structure. Cambridge (Massachusetts) [etc.]: MIT, 1991.

Cita MLA (9a ed.)

Helpman, Elhanan, y Paul R. Krugman. Trade Policy and Market Structure. MIT, 1991.