# How many ephemeral stacks are required to simulate a queue in worst-case $O(1)$ time?

In "Real Time Queue Operations in Pure LISP" (ML implementation), Hood and Melville show an $O(1)$ worst-case simulation of a queue using 6 stacks and global rebuilding. Can a real-time queue be simulated with fewer stacks?

In "Simple and Efficient Purely Functional Queues and Deques", Okasaki shows an implementation using one stack and two lazy stacks.

Both Okasaki's and Hood & Melville's queues require purely functional stacks as building blocks, and both produce purely functional queues. If push and pop are destructive, can global rebuilding be used to simulate an ephemeral queue with 6 ephemeral stacks? Fewer?