Clausen's formula

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In mathematics, Clausen's formula, found by ThomasClausen  ( 1828 ), expresses the square of a Gaussian hypergeometric series as a generalized hypergeometric series. It states

Thomas Clausen (mathematician) Danish mathematician and astronomer

Thomas Clausen was a Danish mathematician and astronomer.

In particular it gives conditions for a hypergeometric series to be positive. This can be used to prove several inequalities, such as the Askey–Gasper inequality used in the proof of de Branges's theorem.

In mathematics, the Askey–Gasper inequality is an inequality for Jacobi polynomials proved by Richard Askey and George Gasper (1976) and used in the proof of the Bieberbach conjecture.

In complex analysis, de Branges's theorem, or the Bieberbach conjecture, is a theorem that gives a necessary condition on a holomorphic function in order for it to map the open unit disk of the complex plane injectively to the complex plane. It was posed by Ludwig Bieberbach (1916) and finally proven by Louis de Branges (1985).

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