Iβve also seen β as the differential operator and πΌ(X) as the expected value of X. I think Iβve also seen π_x, and β , and β but I donβt remember for what.
I know π_X as the indicator function (also called characteristic function) of X in measure theory and probability theory, but Iβve also seen 1_X or Ο_X.
β and β can be basis vectors or imaginary units although Iβve never seen them in blackboard bold in my lectures.
