factor cause SML into a band rather than a line:

when equtual borrowing and lending rate assumption is relaxed, the SML will turn into a band. when say it is a band, what it looks like? and why it turn into a band? Thanks

because for each stock you would have 2 interpretations one using the borrowing rate one with the lending rate causing 2 ‘extreme’ prices that would follow the sml. therefore the sml would not longer be a line but more like a band.