The one value the report list, the TOC and step 1 share: set_report_population()
writes it, makes the analysis data of the set's subjects (adsl_<set>)
when there is none, and moves the report's analyses from the set it had
to the new one: the data of the old set's subjects, and the data kept to
them, to the new set's (found, or made with the same definition); an
analysis of a dataset and the old set to the new set. An analysis data
of another kind (made from another analysis data, written as R) is left
as it is and named in attribute left. Analysis data are the study's:
none is removed.