@article{10_4064_aa_33_1_1_9,
     author = {M. Kenku},
     title = {Atkin-Lehner involutions and class number residuality},
     journal = {Acta Arithmetica},
     pages = {1--9},
     publisher = {mathdoc},
     volume = {33},
     number = {1},
     year = {1977},
     doi = {10.4064/aa-33-1-1-9},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa-33-1-1-9/}
}