APA (7th ed.) Citation

Piwnik, J., Gonera, J., & Kosiński, P. Fermat's principle in general relativity via Herglotz variational formalism. Elsevier.

Chicago Style (17th ed.) Citation

Piwnik, Joanna, Joanna Gonera, and Piotr Kosiński. Fermat's Principle in General Relativity via Herglotz Variational Formalism. Elsevier.

MLA (9th ed.) Citation

Piwnik, Joanna, et al. Fermat's Principle in General Relativity via Herglotz Variational Formalism. Elsevier.

Warning: These citations may not always be 100% accurate.