An observer B is receiving light signals from two patches (A and C) of the CMB. We assume that the light was emitted by these sources at cosmic time t_e, when their proper distances from the observer were R_BA(t_e) and R_BC(t_e), respectively. In addition, we assume that A emitted an earlier light signal at time t_∗ that reached C, a proper distance R_AC(t_e) away, at time t_e.