|Covid-19|Glaeser's continuity theorem Wikipedia
In mathematical analysis, Glaeser's continuity theorem, is a characterization of the continuity of the derivative of the square roots of functions of class
. It was introduced in 1963 by Georges Glaeser, and was later simplified by Jean Dieudonné.
The theorem states: Let
be a function of class
in an open set U contained in
is of class
in U if and only if its partial derivatives of first and second order vanish in the zeros of f.