Complex sentence: Given some inclusion space, an "abstractive class" is a class "G" of regions such that "G" is totally ordered, and there does not exist a region included in all of the regions included in "G".
Split into simpler sentences: Given some inclusion space, an abstractive class is a class "G" of regions such that "G" is totally ordered. Moreover, there does not exist a region included in all of the regions included in "G".