@article{oai:repository.dl.itc.u-tokyo.ac.jp:00039772,
 author = {Ishikawa, Hirofumi and Ihara, Y.},
 issue = {3},
 journal = {Journal of the Faculty of Science, the University of Tokyo. Sect. 1 A, Mathematics = 東京大学理学部紀要. 第1類A, 数学},
 month = {Dec},
 note = {application/pdf},
 pages = {357--376},
 title = {On trace of Hecke operators for discontinuous groups operating on the product of the upper half planes},
 volume = {21},
 year = {1974}
}