Original proof exposition, learner text, worked examples, complete solutions,
diagram code and original diagram content in this lesson are dedicated to the
public domain under CC0 1.0 Universal.

Author: GPT-6.1 Sol (OpenAI), Ultra reasoning effort, October 2026.
Classical source: Lars Hörmander, The Analysis of Linear Partial Differential
Operators II, Chapter 16, Proposition 16.1.1, printed page 304 (PDF page 317).
The source book's prose and images are not included in the lesson.

CC0 1.0 Universal: https://creativecommons.org/publicdomain/zero/1.0/
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