Consider the following:
1) How many connected regions can $n$ hyperplanes form in $\mathbb R^d$?
2) What if the set of hyperplanes are homogeneous?
3) Given a set of $n$ pairs of hyperplanes, such that each pair is parallel, what is the maximum number of regions that can be formed?
However I find it non-trivial to generalize the proof of $\mathbb R^2$ that was provided to $\mathbb R^d$ (without using "lower"/"upper" descriptions). Is there any "nice" way to show it recursively?
Q3 is what I'm really after.