Solution
= Solution
Apply <Itô formula> to $V(t,S_t)$. Its Brownian coefficient is
$$
\sigma S_t\frac{\partial V}{\partial s}(t,S_t).
$$
The self-financing portfolio's Brownian coefficient is $\pi_t\sigma S_t$. Since $S_t\sigma>0$, equality of the two value processes forces
$$
\boxed{\pi_t=\widetilde V(t,S_t),
\qquad
\widetilde V(t,s)=\frac{\partial V}{\partial s}(t,s).}
$$
Thus the stock holding is the claim's <option delta>.