Whenever you then arrange the portfolio all over again by borrowing $S_ t_1 $ at amount $r$ it is possible to realise a PnL at $t_2$ of $begingroup$ Assuming that you're Doing work for just a bank, you can find a few different P&Ls dependant upon the functionality/ usage: It's https://www.youtube.com/watch?v=qMmsQ4kKgY4