= Joseph Bertrand
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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>. https://mathshistory.st-andrews.ac.uk/Biographies/Bertrand/[University of St Andrews historical biography, mathematical work and career]{ref}
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