In: Advanced Math
Assume that ψ : [a, b] → R is continuously differentiable. A
critical point of
ψ is an x such that ψ'(x) = 0. A critical value is a number y such
that for at
least one critical point x we have y = ψ(x).
(a) Prove that the set of critical values is a zero set. (This is
the Morse-Sard
Theorem in dimension one.)
(b) Generalize this to continuously differentiable functions R →
R.