# 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.