I was reading the following article: https://www.researchgate.net/publication/305025128_Can_the_Efficiency_of_an_Arbitrary_Reversible_Cycle_be_Equal_to_the_Efficiency_of_the_Enclosing_Carnot_Cycle_Part_B
Right at the end in the conclusion, the following statement is made:
"Since we already showed above that the efficiency of cycle in Fig. 4 is equal to the efficiency of the enclosing Carnot cycle, it follows that if the efficiency of a reversible cycle is less than the efficiency of the enclosing Carnot cycle, then it is also possible for the efficiency of a reversible cycle to be more than the efficiency of the enclosing Carnot cycle."
How does that make sense? Why must it be possible for the reverse of a statement be true if the statement is true?
I was trying to find an answer to the following question:
Why the most efficient heat engine (carnot cycle), consists of 4 stages, 2 adiabatic ones and 2 isothermal ones. I can't seem to find a proof on why this is the most efficient thermodynamic cycle for a engine, only that if we assume a greater efficiency, we get trouble.