Should a variable denoting a vector always be in upright font, even when it is a Greek letter?
When denoting vector variables, I have noticed that it is common to use a bold, non-italic, lowercase character, such as a, b, etc. I use latex for the few equations I write and I have noticed that it is quite cumbersome to create non-italicized lowercase Greek letters. This makes me wonder if Greek letter variables always should be italicized and it would be wrong to force an upright Greek letter for a vector variable.
What is the preferred way of typesetting a vector variable when it is represented by a Greek character? Should it be in italics and bold, or upright and bold?
Examples, from left to right: upright, bold+upright, italic, italic+bold. The upright letters are using a slightly different font in this example.