[chaley]

Originally Posted by DrChiper

I knew you would come up with a cleverer solution

And indeed, series could have not an index of 1. My improvement would be (I like to keep code small):

series:true and series_index:"<=1"

This will find 0, 0.n and 1.

But what if the first book is missing? The series could start with the second book (index == 2).