Been getting my head wrapped around sequences. I think I've got it.
There are two kinds of thematic sequence. For lack of better terms, I call one the Variation Pair Sequence, and the second the Variation-Type Sequence. Alternative names could be the Progressive Sequence and the Structural Sequence.
Three Act Structure (Signposts):
The Variation Pair Sequence takes the Quad of Variations that contains the Issue for the through line and does an exhaustive compare of all the variations in the list, so you get six appreciations, and then you use two per act in the three act structure, one always containing the issue, and the other one, not. How you arrange these Variation Pairs of the Sequence (the appreciations) will create the effect of progress, growth and change. One way to use them is as you arrive at the Signpost, whew, you look at where you were, and where you are now, and how that affects the view of the Issue.
Four Act Structure:
The Variation-Type Sequence compares the Type for each Act in the four act structure with one of the variations in the quad, so you get four appreciations per act, Type-To-Variation, or sixteen appreciations in the Variation-Type Sequence. The progression effect is caused by the change in the Type, as the through line's Type progresses through its changes.
I actually had to parse and rewrite 18.104.22.168.7 in order to understand this, but I know it would be the height of hubris to post my rewrite here, so I shan't.
Anyway, it's all right there in the book, I just feel like pulling it out a little and underlining it helped my understanding. Let me know where I have erred, please!
I might even consider calling them the
Variation Pair Appreciation Sequence
Variation-Type Appreciation Sequence
for further clarity, even if it's a bit wordy.