APA (7th ed.) Citation

Von Westphalen, J., Marx, K., & Engels, F. Cartas a Kugelmann.

Chicago Style (17th ed.) Citation

Von Westphalen, Jenny, Karl Marx, and Federico Engels. Cartas a Kugelmann.

MLA (8th ed.) Citation

Von Westphalen, Jenny, et al. Cartas a Kugelmann.