@article{AM2_1997__53_1-2_137676,
     author = {P.K. Sahoo and J. Chung and P. Kannappan},
     title = {On trigonometric functional equations of rectangular type.},
     journal = {Aequationes mathematicae},
     pages = {36--53},
     year = {1997},
     volume = {53},
     number = {1-2},
     zbl = {0901.39007},
     url = {http://geodesic.mathdoc.fr/item/AM2_1997__53_1-2_137676/}
}