Separation scenarios for collections of 2-discs immersed in a 4-manifold

In this second out of three talks, we will survey how to deal with three increasingly difficult situations where one wants to separate collections of 2-discs immersed in a 4-manifold. The first situation consists on the separation of 2 collections (by Casson), the second consists on the separation of finitely many discs (by Quinn), and the third consists on the separation of infinitely many discs (by Quinn). The last two situations will make use of the transverse spheres lemma presented in the first talk.