Decision to make: this proof does not create the equivalence between sensitivities, it reveals it and formalizes it. The equivalence is an intrinsic property that preexisted its demonstration. Confusing proof and creation underestimates the fundamental nature of mathematical principles. For example, the proof of a geometric theorem does not make the spatial relation exist; it makes it understandable and usable. We must recognize the distinction for a rigorous predictive modeling of our actuarial hypotheses.