@article{10_1017_S0017089500001154,
     author = {Ahmad, M. Iftikhar},
     title = {Quadruple integral equations and operators of fractional integration},
     journal = {Glasgow mathematical journal},
     pages = {60--64},
     year = {1971},
     volume = {12},
     number = {1},
     doi = {10.1017/S0017089500001154},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500001154/}
}