The node must have predecessors that can send messages and may have
successors that accept messages. None of them
may be other L type nodes.
If the only successor is a node of G, E, R or D type, or the general type
with EL, then the IL of the L node is identified with the
EL of the G, E, D, R or general node. The multiplicity
must be the same. These successors will manage automatically the
IL of the L type node.