 In this section, the notation formula_57 will be used to denote the "k"-factor from Alice to Bob (and similarly between other pairs of observers).As before, Alice sends a blue flash towards Bob and Ed every formula_8 seconds, by her clock, which Bob receives every formula_59 seconds, by Bob's clock, and Ed receives every formula_60 seconds, by Ed's clock.Now suppose that whenever Bob receives a blue flash from Alice he immediately sends his own red flash towards Ed, once every formula_59 seconds by Bob's clock, so Ed receives a red flash from Bob every formula_62 seconds, by Ed's clock.