Deleting Other Established Information
As with subjects any data which have been established can be deleted, and any changes in already established data can be signalled using は:
あした パーティ に いく か
"[Are you] going to the party tomorrow?"
"Yeah, how about you?"
"No, I'm not going."
その あと の えいが は
"How about the movie afterwards?"
This is pretty much how all anaphoric deletions work in Japanese whether it be subjects, objects, or something else. In general, always attempt to delete if possible. This section should also give you a feel for the use of は in normal speech.