no. 3
On momentum states in quantum mechanics
Annales de l'institut Henri Poincaré. Section A, Physique Théorique, Tome 20 (1974) no. 3, pp. 291-296 
@article{AIHPA_1974__20_3_291_0,
     author = {Fannes, M. and Verbeure, A. and Weder, R.},
     title = {On momentum states in quantum mechanics},
     journal = {Annales de l'institut Henri Poincar\'e. Section A, Physique Th\'eorique},
     pages = {291--296},
     year = {1974},
     publisher = {Gauthier-Villars},
     volume = {20},
     number = {3},
     mrnumber = {391782},
     language = {en},
     url = {https://www.numdam.org/item/AIHPA_1974__20_3_291_0/}
}
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Fannes, M.; Verbeure, A.; Weder, R. On momentum states in quantum mechanics. Annales de l'institut Henri Poincaré. Section A, Physique Théorique, Tome 20 (1974) no. 3, pp. 291-296. https://www.numdam.org/item/AIHPA_1974__20_3_291_0/

[1] J. Manuceau, M. Sirugue, D. Testard, A. Verbeure, The smallest C*-algebra for canonical commutation Relations; preprint Marseille 71/p. 397: Comm. Math. Phys., t. 32, 1973, p. 231. | Zbl | MR

[2] J. Von Neumann, Math. Ann., t. 104, 1931, p. 570. | Zbl | JFM

[3] M. Sirugue, Improper States of canonical commutation Relations for a finite number of degrees of freedom; Marseille preprint 71/p. 412.