Ross,
Because there is no need for it. When the vectors (bold) i, j, k are defined to be the standard basis vectors, then they are already unit vectors. Putting a hat over them is quite superfluous. That there is no easy way to do this in Unicode is surely indicative that standard usage does not require it, so you should be discouraged from attempting to do so.
Somewhat off-topic, but math notations cannot follow strict rules and you may want a hat over any i or j -- perhaps a special basis (eg, a rotating one). You can find the hat (with the dot) for example in Schaum's Continuum Mechanics, by Mase. Redundancy, when consistency is also important, is not always a bad thing. Regards Javier -------------------------------------------------- Subscriptions, Archive, and List information, etc.: http://tug.org/mailman/listinfo/xetex
