Name is misleading
A multimap is a K -> Set<V> mapping.
[^0]: As usual with C++ data-structures, order is imposed to keep things "nice" and slower than they should.
This has been pointed out before. What do you propose we do about it?
I think that the readme should begin saying this is not a true multimap. Right now it introduces why it exists and how it works, and then people figures out this is not what they thought.
The project should be ideally also renamed. Now, on what name to take I don't want to impose a name. It'd be ideal if it described the data structure. Initially I was thinking about something to do with aliases, but since the underlying container map is (K1, (K2, V)) and not just (K1, V) it's not just a map with multiple aliases (data: K1->V, aliases: K2->K1).
You can't rename a crate that has been published on crates.io - the name is what it is.
If you want to propose alternative words for the README I'm happy to review the PR.