Empty lists are ... strange, to a Prolog beginner like myself. I would say that it isn't possible to write an empty list [] as a difference list T1-T2 just as it isn't possible to write an atom as a difference list. However, I would guess that to use recursion, there must be a way to use [] in a difference list setting. I have Google'd for this but I cannot find an answer, and Bratko (Prolog Programming for AI) only briefly touches the subject.
So, is it possible to write an empty list as a difference list in Prolog, if so how and when would it be useful?
Problems with understanding this topic are typically due to using misleading terminology.
As recommended in tutorial.pdf and especially pap95.pdf, use for example list difference or simply difference.
Section 5 of Teaching beginners Prolog contains relevant reasons for this.
The empty list is uniquely denoted by the atom [].
Note that a list difference always means reasoning about two lists, and due to this categorical difference between a single and multiple lists, you can at best find some correspondence or analogy, but not identity between the empty list and a list difference.
I completely support the view expressed in the paper above that you should focus on using DCGs, at least at first. Reasoning about differences explicitly will come naturally later to you.