@article{EJDE_2011__2011__a27,
     author = {Littlejohn,  Lance L. and Zettl,  Anton},
     title = {The {Legendre} equation and its self-adjoint operators},
     journal = {Electronic journal of differential equations},
     year = {2011},
     volume = {2011},
     zbl = {1417.34206},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2011__2011__a27/}
}