eliminate code duplication due to module imports

[JonathanAldrich]

When modules are imported multiple times, it appears that sometimes code from these modules is pasted into the program expression multiple times, rather than referring to a single canonical place. We should eliminate this duplication.

[JonathanAldrich]

I think I was able to reduce (and maybe eliminate?) this duplication a while ago. At this point this is not a major issue; it can wait until the back end is refactored.