For a long time (since I first heard of it around 1990), I thought that the terminology “Property (T)” was a completely arbitrary name, and no better than the thousand notions of *“admissible thingummy”* or *“good khraboute”* which sprinkle too many mathematics papers. Then I learnt a few years ago that the “T” was supposed to refer to the **T**trivial representation, since — in a suitable language — the property is about the trivial representation of a group .

This was already better. But much more recently, I learnt from S. Mozes that the typography “(T)” itself was *not* some random choice, but was meant to express the fact that the trivial representation is supposed to be alone in some open set, incarnated as an open interval (so one should read as in )…

A direct corollary is that the right translation in French is, of course, Property .

By the way, I personally much prefer the , , , etc, notation for intervals, but I’m told that many find this ugly beyond belief and much prefer the , , etc, style…