If it's being transferred over the internet, it's a file.
Electronic books are a subset of files, not a disjoint set, just as paper books are a subset of "paper with ink on it".
> Electronic books are a subset of files
follow from
> paper books are a subset of "paper with ink on it"
?
I'd argue that paper books are not a subset of paper files, therefore, in online realm also electronic books should NOT be a subset of electronic files. It is a disjoint set by your logic.
