Hm. Now I wonder where I got the idea that of course it's supposed to be upright. Though I have been reading the Princeton Companion book mentioned in sibling.

Hm. Now I wonder where I got the idea that of course it's supposed to be upright. Though I have been reading the Princeton Companion book mentioned in sibling. I guess the problem is that the system drops the space between the expression and the dx, outputting the "xdx". Math text does have space before dx even if the letter is italic.