I was reading some lecture notes on super-symmetry (http://people.sissa.it/~bertmat/lect2.pdf, second page). It is stated that ". In order for all rotation and boost parameters to be real, one must take all the Ji and Ki to be imaginary". I didn't understand the link between the two. What does imaginary generators have to do with getting real parameters? By parameters, do we mean the ones that appear in the group element as exponential of the generator, or the ones used when deriving the fundamental representation of these generators (see: https://www.classe.cornell.edu/~pt267/files/notes/FlipSUSY.pdf, page 3, phrase after (2.16) to understand what I mean)?