 Solution

The successive abstract sequences are $[10]$, $[20,10]$, $[20,10,30]$, $[10,30]$, $[10,30,40]$, $[10,30,40,10]$, $[10,30,40]$, $[10,30,40,15]$, and finally $[30,40,15]$. The three removals return $20$, $10$, and $10$, respectively. With the display convention in part (i), the output isThe capacity-four bound is never exceeded. The abstract trace is independent of which physical array slots wrap around.