Most people join at the first opportunity they can. However, some schools do not let people join right away. It's often called 'deferred rush.' The school may prohibit people from joining until they have achieved a certain number of credits, or until the second semester or second year.

Even if a school has deferred rush, it doesn't hurt fraternities to get their names out to new students… so that's why it may seem like they are targeting freshmen, even if freshmen at that school cannot join.invol

♣ tailor is a particular case of laurent when given z0=0;
♦ you could prefer Laurent if you want to expand radius of convergence;