thanks for the pointing...I did not have the chance to check out hn at the time...
seems that currently hn uses url as the sole criterion to identify duplicate topics; but I guess one of the alternatives to that would be to use some semantic based features to merge equivalent topics unto a same topic thread -- but then in that case, it would all depend on how we define equivalence...
https://news.ycombinator.com/item?id=15825700