2 gamma physics versus 1 gamma physics and whatever lies in between

Presents the results of some calculations of electromagnetic 2 gamma reactions in various configurations and compares them with corresponding 1 gamma signals or signals from processes that in their turn can be a rather bad background to 2 gamma physics. The author starts by outlining the method by which these calculations were performed. The next section devoted to the study of various final state configurations of the reaction e/sup +/e/sup -/ to e/sup +/e/sup -/ mu /sup +/ mu /sup -/ and, where possible, comparison with 1 gamma final states. The author then discusses problems that can arise in double-tag experiments owing to the presence of Bhabha scattering and its radiative corrections. The contribution to the reaction of e/sup + /e/sup -/ to e/sup +/e/sup -/ mu /sup +/ mu /sup -/ due to diagrams of the non-peripheral type is also investigated. (6 refs).