We depict this in Figure 20. This also consists of two parts (which must be handled separately):
Figure 20 depicts a situation close to the general case. Namely, that each particle has distinct values of: (1) emitting surface for this event step, (2) emission point for this event step, (3) originating surface, and (4) emission direction. The words ``emitting'' and ``emission'' in points (1) and (2) are italicized, as they represnt either a ``birth'' if this is the first event for this particle or a reflection if the event time for this particle is beyond the ``birthing'' event, while in point (3) ``originating'' represnents the ``birthing'' event.