APA (7th ed.) Citation

Firstov, S., & Rogul, T. Theoretical (ultimate) hardness.

Chicago Style (17th ed.) Citation

Firstov, Sergey, and Tamara Rogul. Theoretical (ultimate) Hardness.

MLA (9th ed.) Citation

Firstov, Sergey, and Tamara Rogul. Theoretical (ultimate) Hardness.

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