Corollary
Tag 0852, permanent. Cite it as [Bourbaki, Tag 0852].
Functions of a Real Variable, chapter I, § 3. DERIVATIVES OF HIGHER ORDER
If is a finite real function with a derivative of order on I, and if on I, then for all in I one has
and the second term cannot be equal to the first (resp. to the third) unless is constant and equal to (resp. ) on the interval .
The proof proceeds in the same way, but applying th. 1 of I, p. 14.
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.
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