For better or worse that's very common. A big part of learning to read advanced math is keeping track of the "kind of thing" each variable is meant to be. If yo

For better or worse that's very common. A big part of learning to read advanced math is keeping track of the "kind of thing" each variable is meant to be. If you do that, then overloading D is a convenience which illustrates similarities. But if you're not a professional mathematician then such overloading is terrifically confusing. Actually, I'm fairly certain it still is even for professional mathematicians.