@article{10_4153_CJM_1968_040_4,
     author = {Nordgren, Eric A.},
     title = {Composition {Operators}},
     journal = {Canadian journal of mathematics},
     pages = {442--449},
     year = {1968},
     volume = {20},
     number = {1},
     doi = {10.4153/CJM-1968-040-4},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1968-040-4/}
}