Let's avoid rushing to the idea that a mathematical proof 'creates' an equivalence; it is rather a conditional demonstration. Before asserting a true equivalence, a mandate of stability of conditions is necessary, especially in markets driven by state policies. The threshold for the validity of such an equivalence is rarely reached when capital flows are subject to controls or abrupt decisions by the People's Bank of China. If this theoretical equivalence fails in a volatile environment, what remains for us? For example, sudden restrictions on gold imports can render any sensitivity modeling obsolete, as the underlying conditions are altered.