Fix some typos, etc., in comments.

[ci skip]

compiler/types/CoAxiom.hs

@@ -223,7 +223,7 @@ data CoAxBranch
     , cab_tvs      :: [TyVar]       -- Bound type variables; not necessarily fresh
     , cab_eta_tvs  :: [TyVar]       -- Eta-reduced tyvars
                                     -- See Note [CoAxBranch type variables]
-                                    -- cab_tvs and cab_lhsmay be eta-reduded; see FamInstEnv
+                                    -- cab_tvs and cab_lhs may be eta-reduded; see
                                     -- Note [Eta reduction for data families]
     , cab_cvs      :: [CoVar]       -- Bound coercion variables
                                     -- Always empty, for now.

compiler/types/FamInstEnv.hs

@@ -615,10 +615,11 @@ If we're not careful during tidying, then when this program is compiled with
     axiom DataFamilyInstanceLHS.D:R:SingMyKind_0 ::
       Sing _ = DataFamilyInstanceLHS.R:SingMyKind_ _
 
-Its misleading to have a wildcard type appearing on the RHS like
-that. To avoid this issue, during tidying, we always opt to add a
-numeric suffix to types that are simply `_`. That way, you instead end
-up with:
+It's misleading to have a wildcard type appearing on the RHS like
+that. To avoid this issue, when building a CoAxiom (which is what eventually
+gets printed above), we tidy all the variables in an env that already contains
+'_'. Thus, any variable named '_' will be renamed, giving us the nicer output
+here:
 
   COERCION AXIOMS
     axiom DataFamilyInstanceLHS.D:R:SingMyKind_0 ::
@@ -626,7 +627,9 @@ up with:
 
 Which is at least legal syntax.
 
-See also Note [CoAxBranch type variables] in CoAxiom
+See also Note [CoAxBranch type variables] in CoAxiom; note that we
+are tidying (changing OccNames only), not freshening, in accordance with
+that Note.
 -}
 
 -- all axiom roles are Nominal, as this is only used with type families