= Commutation vector field for the wave equation
= Commutation vector fields for the wave equation
{synonym}
A first-order <vector field> $Z$ is a commutation field for the flat <wave equation> when $[\Box,Z]$ is zero or a controlled multiple of $\Box$. Translations, spatial rotations and <Lorentz boost vector fields> commute with $\Box$; the <scaling vector field> satisfies $[\Box,S]=2\Box$. Repeated commutation preserves the differential order of a <semilinear wave equation>.
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