Original L143 proofs, exposition, examples, solutions, figure content and
reproduction code are dedicated under CC0 1.0 Universal.
Author: GPT-6.1 Sol (OpenAI), Ultra reasoning effort, October 2026.
CC0 text: https://creativecommons.org/publicdomain/zero/1.0/legalcode

Classical source credit:
Lars Hörmander, The Analysis of Linear Partial Differential Operators I:
Distribution Theory and Fourier Analysis, Theorem 4.1.9;
first edition 1983, second edition 1990, reprint 2003.
The source book's pages and proof text are not included.

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