On a star-shaped neighbourhood of , a smooth function satisfies
The fundamental theorem of calculus along the segment proves the identity, and differentiation under the integral sign proves smoothness of the coefficients.
For a smooth function ,
where the smooth remainder is

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Hadamard's lemma is a result in the field of differential calculus that relates to the expansion of a function in terms of its derivatives. Specifically, it provides a formula for expressing the value of a function at a point in terms of its Taylor series expansion around another point.