Lebesgue's lemma
For Lebesgue's lemma for open covers of compact spaces in topology see Lebesgue's number lemma
In mathematics, Lebesgue's lemma is an important statement in approximation theory. It provides a bound for the projection error.Statement
Let be a normed vector space, U a subspace of V, and P a linear projector on U. Then for each v in V:
