@article{paperid:1029233, author = {Hejazian, Shirin and Mahdavian Rad, Hussein and Mirzavaziri, Madjid and Mohammadian, Hossein}, title = {Bi-parameter Semigroups of linear operators}, journal = {Electronic Journal of Theoretical Physics}, year = {2012}, volume = {9}, number = {26}, month = {January}, issn = {1729-5254}, pages = {173--182}, numpages = {9}, keywords = {One Parameter Semigroup; Bi-parameter Semigroup; σ-derivation; Infinitesimal generator}, }