“…In this section, we will give a brief outline of some of the main features of the Rudge-Seaton-Peterkop (RSP) theory. The mathematics is quite involved and it is certainly not our intention to give a complete discussion, for which the reader is referred to the original papers [14][15][16], and the extended discussion we have given elsewhere [17][18][19]. It is shown in Rudge, Seaton and Peterkop [14][15][16] that the direct amplitude for (e, 2e) on hydrogen may be written,…”