Benes's Formula for M/G/1-FIFO "Explained" by Preemptive-Resume LIFO

We provide a term-by-term interpretation of Benes's well-known but mysterious inversion of the Pollaczek-Khintchine formula. The strategy is to recognize the equality of waiting time in M/G/1-FIFO with remaining work in M/G/1-LIFO-preemptive resume. In the process, we give a new and simple derivation of some known results for M/G/1-LIFO-preemptive resume.