@article{CMH_1931__3_138554,
     author = {G. P\'olya and M. Plancherel},
     title = {Sur les valeurs moyennes des fonctions r\'eelles d\'efinies pour toutes les valeurs de la variable.},
     journal = {Commentarii mathematici Helvetici},
     pages = {114--121},
     publisher = {mathdoc},
     volume = {3},
     year = {1931},
     zbl = {57.0298.03},
     url = {http://geodesic.mathdoc.fr/item/CMH_1931__3_138554/}
}