Why do we always talk about the Carnot cycle as being the most efficient, ideal engine? Doesn't the same equation hold for any reversible heat engine operating between two thermal reservoirs? Couldn't you prove e = 1-T[itex]_{L}[/itex]/T[itex]_{H}[/itex] for any reversible cycle? And then you can apply the usual "no perfect refrigerator" argument to show that this must be the maximum efficiency for a reversible heat engine. What's so special about the Carnot cycle? Is it simply easier to get the above equation from a Carnot cycle, or is it actually the only reversible cycle that reaches this efficiency? Does it have other interesting properties besides being used to prove the above equation in textbooks?