# Time translation symmetry

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A PDE is said to have **time translation symmetry** if for any solution the function is also a solution for all (or some interval of) . Generally speaking, a PDE has time translation symmetry when the coefficients and data do not explicitly involve the time variable t.

A PDE which has time-translation symmetry is also called *time-translation invariant* or *autonomous*.

One can often use time-translation symmetry to bootstrap a local well-posedness result into a global well-posedness one, provided that one has some uniform control on the lifespan of the solution provided by the local well-posedness theory.