mkTcCoVarCo :: EqVar -> TcCoercion
-- ipv :: s ~ t  (the boxed equality type) or Coercible s t (the boxed representational equality type)
mkTcCoVarCo ipv = TcCoVarCo ipv
mkTcCoVarCo :: EqVar -> TcCoercion
mkTcCoVarCo ipv = TcCoVarCo ipv
mkTcCoVarCo ipv = TcCoVarCo ipv