# Italic or upright letters for corners/points in geometry

What is the recommended typeface for "corner points" (e.g. "the triangle ABC"), distances (e.g. "the side AB"), etc. in geometry? Should it be upright or italic? Some say all constants should be upright (even $$e$$ and $$\pi$$) and since "corner points" are constant they should therefore be upright. If a point on a line, say E between A and B, is variable, should it then be in italic, E, to indicate a variable? Any comments and thoughts about this are welcome. TIA.

$$\triangle ABC$$ ...
The question is not whether they are constant. The letter $$A$$ may be different points in different problems, and even in one problem the letter $$A$$ could represent any point in the plane. So, despite being "constant", these are variables, and thus they are set in italic nowadays.
Similarly, we write a line $$y=ax+b$$ where $$a$$ and $$b$$ are constants, and set all four variables $$a,b,x,y$$ in italic.
• Good arguments. It all got me thinking when I saw several national 'SAT'-like tests, spanning 10+ years back, where they put most "mathematical letters" in upright typeface. But, the general quality of the drawings and math in these test are rather low so I would not assume they got the letters right (either). (The tests seems to be made in Word…) I have started to use upright $i$, $e$ and $\pi$ since, apart from being constants, go well with how Mathematica display these constants. However, Mathematica seems to print any constant (integration or diff-eq. solution) as upright…