a) Prove that every finite subset of Rn is a Jordan region of volume zero.
b) Show that, even in R2, part a) is not true if finite is replaced by countable.
c) By an interval in R2 we mean a set of the form
[(x, c) : a < x < b] or {(c, y) : a < y < b)
for some a, b, c ∈ R. Prove that every interval in R2 is a Jordan region.