\begin{code}
module TcUnify where
-import TcType ( TcTauType, BoxyType )
+import TcType ( TcTauType, BoxySigmaType, BoxyType )
import TcRnTypes( TcM )
+import Coercion (CoercionI)
-- This boot file exists only to tie the knot between
-- TcUnify and TcSimplify
-unifyType :: TcTauType -> TcTauType -> TcM ()
-zapToMonotype :: BoxyType -> TcM TcTauType
+unifyType :: TcTauType -> TcTauType -> TcM CoercionI
+boxyUnify :: BoxyType -> BoxyType -> TcM CoercionI
+zapToMonotype :: BoxySigmaType -> TcM TcTauType
\end{code}