After #15050 (closed) and [changeset:"4d91cabc/ghc" 4d91cabc/ghc] it seems odd to call
SigTv for the kind of type variables that used to be used in type signatures in patterns, but are now used in other places (kind signatures, partial type signatures).
SigTv may be associated with sigma. At some point I assumed that
SigTv are type variables that may unify with polytypes, while
TauTv are those that unify with monotypes.
As a service to our future self, I’d like to rename
Best one I have is
TyVarTv (for a type variable that stands for a type variable).