Funny, while reading about how lowercase L, capital I and numeral 1 all look so similar, I am seeing it in my email font where they're entirely different, and all distinct from the vertical bar. It can be done. Lowercase L, by the way, looks like this: -+ | | | | | \_ What I mean is, that is the actual, true appearance of lowercase L, which has only recently been discovered, apparently. I think in a pinch you can leave off the serif at the top. Here are some modern fixed-width fonts that follow the same conventions for 1, l, I and |, and similar differences between capital O and zero 0. Apple Menlo Bitstream Vera Sans Mono Bera, for use with LaTeX DejaVu Sans Mono I guess the reason there are more fixed-width fonts with these graces is that there are more programmers than mathematicians, and programmers... think of notation as malleable and utilitarian?. Be unambiguous and explicit, I say. That's why I like ln and lg. Also, check out http://www.johndcook.com/blog/2013/04/23/why-j-for-imaginary-unit/ . --Steve