A local diffeomorphism restricts near every point to a diffeomorphism onto an open subset. In particular, every local diffeomorphism is an open map.
The displayed smooth map from to the punctured plane has Jacobian determinant one: in polar coordinates its radius is and its angle is , so the determinant is . Nevertheless for every integer . Thus a local volume-preserving map need not be injective or have bounded weighted inverse multiplicity. Compactly supported data distributed over many inverse branches disprove a determinant-only dispersion with a nonlinear velocity map estimate.
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A **local diffeomorphism** is a mathematical concept from differential geometry that describes a type of smooth map between two differentiable manifolds (or smooth manifolds).