Proof of Fermat and Huygens–Fresnel principle

[Nick Jackson]

Hey guys, I don't know if here is the right section for this question but anyway. So I was looking for the proof or derivation of the Fermat's principle and all I got was the Huygens–Fresnel principle. However, neither could I understand how the Huygens–Fresnel principle derives the Fermat's principle nor how one can derive or prove the Huygens–Fresnel principle.
Any help is welcome!
Thanks

 

[UltrafastPED]

Fermat's principle of least time can be used with the calculus of variations to derive the eikonal equation. The eikonal equation is in turn equivalent to the Huyghen's wavelet mechanism.

See this thread: https://www.physicsforums.com/showthread.php?t=752726