Let f be a function with domain the reals and range the reals.
Assume that f has a local minimum at each point x in its domain.
(This means that, for each x ∈ R, there is an E = Ex > 0 such
that, whenever | x−t |< E then f(x) ≤ f(t).) Do not assume that
f is differentiable, or continuous, or anything nice like that.
Prove that the image of f is countable. (Hint: When I solved...