We give a new characterization of SOP (the strict order property) and an
optimal version of a theorem of Shelah, namely a theory has OP (the order
property) if and only if it has IP (the independence property) or SOP. We point
out some connections between dividing lines in unstable theories and subclasses
of Baire 1 functions.Comment: In this new version there are some necessary functional analysis
  background,and minor corrections. (21 pages