[ghkbrew]

Well no actually it'd still clear to me that they mean the the multiplication of 3 different variables X, N, and D.

I don't think of it as eliding obvious operators. Rather in mathematics juxtaposition is used as an operator to represent multiplication. You would never elide an addition operator.

So X next to D still means multiplication as long as you can tell that X and D are separate entities.

I would wonder why they switched conventions in the middle of an expression though.

[Quarrelsome]

> Well no actually it'd still clear to me that they mean the the multiplication of 3 different variables X, N, and D.

Sure, but its not clear to me. I'm just cross about implied convention in maths.