 Joseph Bertrand

A French mathematician whose work ranged across number theory, differential geometry and probability theory. His 1845 prime-number conjecture became Bertrand's postulate: for every integer $n>1$ there is a prime number strictly between $n$ and $2n$. The result is a theorem, rather than an unproved conjecture, despite its traditional name.

Bertrand's paradox illustrates a different part of his legacy: an instruction to choose a random chord does not define a unique probability distribution until the sampling rule is specified. His career also included teaching analysis in Paris and writing textbooks in calculus and mathematical physics. ^[ref]

Joseph Bertrand (1822–1900) was a French mathematician known for his contributions to several areas of mathematics, particularly probability theory and mathematical analysis. He is perhaps best known for Bertrand's Paradox, which addresses a problem in geometric probability and illustrates the ambiguities that can arise in probability theory. In addition to his work in probability, Bertrand made contributions to number theory and is known for the Bertrand's Postulate (now proven and known as the Bertrand–Chebyshev theorem).