See invariant estimator for background on invariance or see equivariance. The Lagrangian formulation makes the relativistic invariance apparent. Such geodesics are the generalization of the invariance of lightspeed in special relativity. In general relativity, general covariance is intimately related to "diffeomorphism invariance". General covariance is a special case of gauge invariance. Both gauge invariance and diffeomorphism invariance reflect a redundancy in the description of the system. While developing general relativity, Einstein became confused about the gauge invariance in the theory. These desirable properties may be described as&colon; validity, optimality, and invariance. It is unique among the constraint gauges in retaining manifest Lorentz invariance. There are several short proofs of the invariance of this parity of a permutation. Magueijo has also proposed a formulation that preserves local Lorentz invariance. All of them are essentially a direct consequence of the requirement of Lorentz invariance. It is a sophisticated method to deal with quantum physical theories with gauge invariance. These conditions give the model translational invariance, which is useful for analytic study. The invariance of the action follows from the classical invariance of Maxwell's equations.