I have $\phi(x)\sin(nx)$ where $\phi(x)$ is a test function. Obviously, the product is continuously differentiable, but I don't know if $\phi(x)\sin(nx)$ has a compact support too?
2026-04-01 10:04:20.1775037860
Is the product of a continuously differentiable function with a test function also a test function?
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