@article{RCM_1989__23_1-4_181821,
     author = {A. Al-Zamel and R. Khalil},
     title = {Vector valued {Chebechev} systems},
     journal = {Revista colombiana de matematicas},
     pages = {25--34},
     publisher = {mathdoc},
     volume = {23},
     number = {1-4},
     year = {1989},
     zbl = {0718.41034},
     url = {http://geodesic.mathdoc.fr/item/RCM_1989__23_1-4_181821/}
}