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[ShapeOfMatter]

I'm not thrillled with the API or implementation, and I'm only mostly-sure it works. But I'm mostly sure it works!

[ShapeOfMatter]

Re-reading everything today; I don't see any deep ways to improve the ergonomics.

• The tracking of memberships and subsets can be improved, but that's going to involve a deeper understanding of both singletons and Ghosts Of Departed Proofs, so I think we should move forward without it for now.
• A systematic array of helper functions would be better than what we have right now, but will be a small project in itself and I'm not sure we're ready yet to say what helpers we want. ATM there are four copies of locally, depending whether it uses the un argument and whether it returns anything; I'm imagining expanding that style of "grid" across a few more dimensions and cases in a way that's practical to remember. If we want this it should be its own ticket.
• Some of the existing functions could be re-named; e.g. the current unwrap' and `unwrap' make no sense; it's just how it evolved. But I'm not sure this will make the choreographies any easier to read or write.

I think I should merge this, but a review would be nice and I know that'll be easier if I document my work some...

[ShapeOfMatter]

@psilospore I've added some documentation; I've tried to get the formatting right for parsing my IDEs, but mine still isn't showing argument-level comments.

@jnear I've committed the MPC example we were working on today.

Gonna go ahead and merge so we can move on to the next things.