mkTcTransCo :: TcCoercion -> TcCoercion -> TcCoercion
mkTcTransCo (TcRefl {}) co = co
mkTcTransCo :: TcCoercion -> TcCoercion -> TcCoercion
mkTcTransCo (TcRefl {}) co = co
mkTcTransCo (TcRefl {}) co = co