NSManagedObject and Comparable is the solution?

I need to compare two NSManagedObject objects to need if an object is inside in a array.
Extend NSmangedObject class or my custom subclass like Lemma, Kanji that are created by core data, could be the solution to compare two object?

Lemma is subclass of NSManagedObject
var lemma1:Lemma
var lemma2:Lemma

if lemma1 == lemma2 {