\Diagram \frame \phantom {XXX}\endframe \\ & \rdDashto \\ & & \frame \phantom {XX}\endframe \\ \Modify \Line (2,0) (3.2,0) \tl \bullet \jt \hd {(R_r,C_r)} \Math {(R_\ell ,C_r)} (2,2) *{-.2} \Line (0,2) (-1.3,2) \tl \bullet \jt \hd {(R_\ell ,C_\ell )} \Math {(R_r,C_\ell )} (0,0) *{1.2} \Bij (0,0) (2,0) \tl \bullet _{d_\ell } \Bij (0,2) (2,2) \hd \bullet ^{d_r} \endDiagram