Note [GHC Formalism]

This file implements the type-checking algorithm for System FC, the "official"
name of the Core language. Type safety of FC is heart of the claim that
executables produced by GHC do not have segmentation faults. Thus, it is
useful to be able to reason about System FC independently of reading the code.
To this purpose, there is a document core-spec.pdf built in docs/core-spec that
contains a formalism of the types and functions dealt with here. If you change
just about anything in this file or you change other types/functions throughout
the Core language (all signposted to this note), you should update that
formalism. See docs/core-spec/README for more info about how to do so.