Lazar Lyusternik

Lazar Aronovich Lyusternik was a Soviet mathematician. He is famous for his work in topology and differential geometry, to which he applied the variational principle. The theory he introduced, together with Lev Schnirelmann, proved the theorem of the three geodesics, a conjecture by Henri Poincar that every convex body in 3dimensions has at least three simple closed geodesics. The ellipsoid with distinct but nearly equal axis is the critical case with exactly three closed geodesics.

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Source: Wikipedia