Past exam of the year 1 of the computer science course of the University of Oxford / 2021 / Imperative programming (resit) / 4 / d / ii / Solution

With that display format the output isThe first removal takes the newly prepended left value $20$. The right removal later takes the most recently appended $10$. The next left removal takes the earlier $10$, leaving the ordered sequence $⟨30,40,15⟩$. The two equal values are different occurrences, and the displayed order follows the links rather than numerical sorting.