Hello, in the above example the student actually wanted to multiply r0 times the expression in (). Instead, his input was taken as a function. Yet the validation shows such a huge space between r0 and () that he could not have guessed this misinterpretation. I am thinking of adopting a rigid * policy, which would be a pity for numeric results with units though.

I know that the validation always shows multiply with a center dot (default), but the students don't take that as a strict rule and aren't alerted when the dot is missing. 

Sort of question "Do you really mean a function r0()?" would be helpful, perhaps.