The discussion centers on the relationship between the efficiency of thermal engines and the reversibility of processes, particularly during isochoric and isobaric phases. It highlights that while heat transfer in these processes depends solely on temperature changes, the efficiency of an engine can differ based on whether the processes are reversible or irreversible. The Carnot theorem is referenced, indicating that a reversible engine operating between the same temperature limits will have higher efficiency than an irreversible one. Participants debate the correct definition of efficiency, emphasizing that it should account for all heat inputs during a cycle. Ultimately, the conversation reveals complexities in applying theoretical efficiency formulas to practical scenarios involving different process types.