@article{CM_1980__41_2_207_0,
     author = {Casselman, W. and Shalika, J.},
     title = {The unramified principal series of $p$-adic groups. {II.} {The} {Whittaker} function},
     journal = {Compositio Mathematica},
     pages = {207--231},
     publisher = {Sijthoff et Noordhoff International Publishers},
     volume = {41},
     number = {2},
     year = {1980},
     mrnumber = {581582},
     zbl = {0472.22005},
     language = {en},
     url = {http://www.numdam.org/item/CM_1980__41_2_207_0/}
}