`[source] <https://gitlab.haskell.org/ghc/ghc/tree/master/compiler/coreSyn/CoreFVs.hs>`_

compiler/coreSyn/CoreFVs.hs
===========================


Note [The FVAnn invariant]
~~~~~~~~~~~~~~~~~~~~~~~~~~

`[note link] <https://gitlab.haskell.org/ghc/ghc/tree/master/compiler/coreSyn/CoreFVs.hs#L534>`__

Invariant: a FVAnn, say S, is closed:
  That is: if v is in S,
           then freevars( v's type/kind ) is also in S