@article{GMJ_2003__10_1_51147,
     author = {Cassisa, C. and Ricci, P.E. and Tavkhelidze, I.},
     title = {Operational identities for circular and hyperbolic functions and their generalizations.},
     journal = {Georgian mathematical journal},
     pages = {45--56},
     year = {2003},
     volume = {10},
     number = {1},
     zbl = {1055.44008},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/GMJ_2003__10_1_51147/}
}