Is it necessary to include each and every theme?
I'm experimenting writing a theme and variation on the
Schubert Moment Musical in F minor, Opus 94 No 5. It has two distinct themes, one being built around a rhythmic drive, the other being a more introspective theme. Would standard form or whatever dictate that you need to include both themes?
Oh, and repeats? I'm assuming you don't need those (though even if it is supposed to happen I'm not going to do it).
EDIT: Just realized that I probably don't need to, considering I'm picking a single theme and writing variations on that theme.
I might incorporate the other theme into the 4th variation, though.