no. 1
Rotation numbers for diffeomorphisms and flows
Annales de l'I.H.P. Physique théorique, Tome 42 (1985) no. 1, pp. 109-115 
@article{AIHPA_1985__42_1_109_0,
     author = {Ruelle, David},
     title = {Rotation numbers for diffeomorphisms and flows},
     journal = {Annales de l'I.H.P. Physique th\'eorique},
     pages = {109--115},
     year = {1985},
     publisher = {Gauthier-Villars},
     volume = {42},
     number = {1},
     mrnumber = {794367},
     zbl = {0556.58026},
     language = {en},
     url = {https://www.numdam.org/item/AIHPA_1985__42_1_109_0/}
}
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Ruelle, David. Rotation numbers for diffeomorphisms and flows. Annales de l'I.H.P. Physique théorique, Tome 42 (1985) no. 1, pp. 109-115. https://www.numdam.org/item/AIHPA_1985__42_1_109_0/

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[3] D. Ruelle, Ergodic theory of differentiable dynamical systems. Inst. Hautes Études Sci., Publ. Math., t. 50, 1979, p. 275-306. | Zbl | MR | Numdam