[4]

Even less common is the possibility of going to yet a third step, where L2 becomes the object of an experience, L3, the introspection of introspection. Contrary to a first impression this is not infinite regress: since all this is happening in a brief period of time, the levels of examination stop there, since experience shows clearly that L2 is already an effort, and for L3 to appear one needs a highly trained sustained attention!