In the case of phrases like this one: "mit oder ohne dir", which case is "du" supposed to be in? Are both dative and accusative acceptable? If not then how do you determine the right conjugation?
of course "mit" needs the dative and "ohne" the accusative, so by repeating the "du"-part the sentence "mit dir oder ohne dich" is grammatically completely correct. In spoken language you will, however, often find a contraction, which is grammatically not correct, but sounds smoother. In this case you will use the case of the second preposition, i.e. "mit oder ohne dich".