Červený, V. (July 2002). "Fermat's Variational Principle for Anisotropic Inhomogeneous Media". Studia Geophysica et Geodaetica. 46 (3): 567. doi:10.1023/A:1019599204028. S2CID115984858.
Červený, V. (July 2002). "Fermat's Variational Principle for Anisotropic Inhomogeneous Media". Studia Geophysica et Geodaetica. 46 (3): 567. doi:10.1023/A:1019599204028. S2CID115984858.