It is a book which has many couplets, written as a set of ten, categorized under different titles. For instance, there is a set of ten under the title "The decad of mountains" This one has couplets written about mountains.
There is one with the title "The decad of Elephants" However, this one has couplets, not written about elephants, but has reference to "elephants" in each one of them. So, basically, this set of ten simply has the word "elephant" mentioned in them and that is the commonality between them.
Is there a difference between "decad on" and "decad of?"
My understanding of "on" and "of" is as follows:
on mountains - about mountains
of mountains - belonging to mountains
However, these two are used interchangeably by many. Do they have any difference at all?