I found your link, and I shall give it to you in 3 seconds ...

A computer science student and a practical hacker are discussing problems the computer science student has run in to. CS Student: I have this singularly linked tail-queued list and I'm trying to make it O(1) to go backwards an item, instead of O(n)... What's the best way to go about that? Should I just use a cached hash of each item and put it into a sorted lookup table, and cache the hash of the last item in the current queue entry and then go to its place in the hash table and get the pointer value from there? Hacker: No, you should add an item to the structure named 'prev' and make it point to the previous item. CS Student: But we already have a structure element with that identifier and structure elements must have unique names within that scope! Hacker: So call it 'previous'. And then the CS Student was enlightened.