Geodesic
Directional differentiability of the distance function
Sbornik. Mathematics, Tome 186 (1995) no. 3, pp. 337-358

Voir la notice de l'article provenant de la source Math-Net.Ru

In this paper we construct an invariant of integrable Hamiltonian systems with two degrees of freedom (the so-called st-molecule) enabling such systems to be classified on three-dimensional constant-energy surfaces up to orientation-preserving diffeomorphisms taking trajectories into trajectories. 
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     author = {S. I. Dudov},
     title = {Directional differentiability of the distance function},
     journal = {Sbornik. Mathematics},
     pages = {337--358},
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     number = {3},
     year = {1995},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1995_186_3_a2/}
}
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S. I. Dudov. Directional differentiability of the distance function. Sbornik. Mathematics, Tome 186 (1995) no. 3, pp. 337-358. http://geodesic.mathdoc.fr/item/SM_1995_186_3_a2/