... Montgomery1
See Montgomery, R. The $N$-body problem, the braid group, and action-minimizing periodic solutions, Nonlinearity 11 (1998) pp. 363-376.
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... existence2
See Chenciner, A. and Montgomery, R. A remarkable periodic solution of the three-body problem in the case of equal masses. Ann. Mathematics 152 (2000) pp. 881-901.
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