@article{ELMA_1989__44_3_141460,
     author = {David E. Dobbs},
     title = {A characterization of the tangent function.},
     journal = {Elemente der Mathematik},
     pages = {101--104},
     publisher = {mathdoc},
     volume = {44},
     number = {3},
     year = {1989},
     zbl = {0706.26006},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1989__44_3_141460/}
}