The concept of a wave field is introduced to represent oriented media. The wave field is a tensor field of second rank, and directors are its eigenvectors. This exhibition of directors defines a natural gauge group inherent in continua and allows one to derive from a variational principle general relativistic and gauge-invariant equations for the wave field in question. Thus, the gauge-theoretical approach to a continuum with internal degrees of freedom gives rise to an unambiguous and minimally coupled theory. [References: 13]
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