map -package:containers -package:basement -package:psqueues -package:Cabal-syntax -package:conduit -package:aeson -is:exact -package:case-insensitive -package:ghc -is:exact -package:bytestring -package:charset -package:amazonka-core -package:os-string -package:unordered-containers -package:vector -package:text -package:monoidal-containers -package:foldl -package:invertible -package:bloodhound -package:hedgehog package:stm-containers

Hash-table, based on STM-specialized Hash Array Mapped Trie.
Bidirectional map. Essentially, a bijection between subsets of its two argument types. For one value of the left-hand type this map contains one value of the right-hand type and vice versa.
A multimap, based on an STM-specialized hash array mapped trie. Basically it's just a wrapper API around Map key (Set value).