@article{10_4153_CMB_1968_054_1,
     author = {Al-Salam, N.A. and Al-Salam, W. A.},
     title = {Some {Characterizations} of the {Ultraspherical} {Polynomials}},
     journal = {Canadian mathematical bulletin},
     pages = {457--464},
     year = {1968},
     volume = {11},
     number = {3},
     doi = {10.4153/CMB-1968-054-1},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1968-054-1/}
}