= Mark Krein
{c}
{title2=1907-1989}
{wiki}
= Mark Grigorievich Krein
{c}
{synonym}
= M. G. Krein
{c}
{synonym}
<Mark Krein> was a <mathematician> whose research joined <functional analysis>, <linear operator theory>, <harmonic analysis> and <mathematical physics>. He worked on the <moment problem>, <integral equations> and the <spectral theory> of linear operators, building an influential research school despite severe institutional discrimination.https://mathshistory.st-andrews.ac.uk/Biographies/Krein/[Biography, research on moments and operators, Odessa school and dismissals]{ref} The <Krein-Milman theorem>, proved with <David Milman>, gives a geometric expression of this work: a nonempty compact <convex set> in a locally convex Hausdorff space is the closed <convex hull> of its <extreme points>. In finite dimensions, the corresponding picture is a convex polygon reconstructed from its vertices.
https://mathshistory.st-andrews.ac.uk/Biographies/Krein/
\Image[https://mathshistory.st-andrews.ac.uk/Biographies/Krein/Krein.jpeg]
{title=Portrait of <Mark Krein>}
{width=240}
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