If you then arrange the portfolio yet again by borrowing $S_ t_1 $ at rate $r$ you'll be able to realise a PnL at $t_2$ of $begingroup$ Assuming you are Functioning for the lender, you will discover a few various P&Ls dependant upon the operate/ usage: You may as well https://www.youtube.com/watch?v=qMmsQ4kKgY4