Previous submissions:

http://news.ycombinator.com/item?id=3349461

http://news.ycombinator.com/item?id=3355254

AFTER EDIT: Oh, and the previous submission with the most comments:

http://news.ycombinator.com/item?id=3350529

As a few other HN participants before me have done, I note previous submissions (when I notice them myself) partly to figure out the vagaries of the duplicate thread detector here and partly to keep the emphasis here at Hacker News on new stories. Some old stories are very worthy indeed of further discussion, but looking at previous threads and their level of discussion can help busy HN participants who didn't notice the last thread(s) decide how much new discussion to engage in about a previously submitted story.