We can rewrite the stochastic differential equation for $S$ in terms of $X$ as follows:
$$dX = \frac{1}{S}dS - \frac{1}{2}\left(\frac{1}{S}\right)^2d[S]$$
Using Ito's lemma, we can find the stochastic differential equation for $X$:
$$dX = \left(\mu -
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