\ is the Standard notation for a left Slice move, but the last time I've seen someone actually use left and right slice moves during one alg was when the Calvin's was still the number 1 Sq1(which you probably remember judging by your account age), so there won't be too many modern algs utilizing the left slice.
As a fellow lefty, I use the right Slice(or used to, permanent damage makes it nearly impossible for me to complete a Sq1 Ao5)