American-option superhedge with a funded reserve (source code)

= American-option superhedge with a funded reserve
{c}
{title2=$dD_t=(rD_t+a(S_t))dt$}

If a nonnegative value $V$ dominates the payoff and $a=rV-\mathcal L_rV\geq0$, delta holdings $V\prime(S)$ combined with a reserve satisfying $dD=(rD+a(S))dt$ give a <self-financing portfolio> of wealth $V(S)+D$. The reserve retains the surplus instead of consuming it, so the wealth dominates the payoff at every exercise time.