= Diffeomorphism invariance of general relativity
Transforming a <metric tensor> and all matter fields together by the pullback of a <diffeomorphism> preserves the <Einstein field equations> and covariant matter equations. Passive coordinate changes only change the description of the fields; active pullbacks produce another representative of the geometry. The treatment of transformations acting on a boundary depends on the boundary conditions and possible charges. A <diffeomorphism> is not necessarily an <isometry> of a fixed metric.
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