(E1) \(\boldsymbol{f} \circ \id_X = \boldsymbol{f}\),   \(\mathbf{id}_Y \circ \boldsymbol{f} = \boldsymbol{f}\),   \(\boldsymbol{h} \circ   (\boldsymbol{g} \circ \boldsymbol{f}) = (\boldsymbol{h} \circ \boldsymbol{g})  \circ \boldsymbol{f}.\)