APA (7th ed.) Citation

Gregory I, P., Bofarull, J., & Soberanas, A. (1931). Dialegs. Editorial Barcino.

Chicago Style (17th ed.) Citation

Gregory I, Pope, James Bofarull, and Amadeu-J Soberanas. Dialegs. Barcelona: Editorial Barcino, 1931.

MLA (8th ed.) Citation

Gregory I, Pope, et al. Dialegs. Editorial Barcino, 1931.