Any time you then build the portfolio again by borrowing $S_ t_1 $ at level $r$ you could realise a PnL at $t_2$ of WillWill 13344 bronze badges $endgroup$ 4 $begingroup$ Did you not say to begin with that $V$ is self-financing? In that circumstance there isn't a Expense to https://www.youtube.com/watch?v=qMmsQ4kKgY4