fdeqs = zipAndComputeFDEqs (\_ _ -> False) rtys1' irs2'
-- Don't discard anything!
-- We could discard equal types but it's an overkill to call
- -- tcEqType again, since we know for sure that /at least one/
+ -- eqType again, since we know for sure that /at least one/
-- equation in there is useful)
qtvs' = filterVarSet (`notElemTvSubst` subst) qtvs