bs-previous-buffer is a compiled Lisp function in `bs.el'.

(bs-previous-buffer &optional BUFFER-LIST SORTING-P)

Return previous buffer and buffer list for buffer cycling in BUFFER-LIST.
Ignore sorting when SORTING-P is nil.
If BUFFER-LIST is nil the result of `bs-buffer-list' will be used as
buffer list. The result is a cons of last element of BUFFER-LIST and the
buffer list used for buffer cycling.