an event type in which one participant acts upon another participant, and the second participant acts on a third participant in the same way, and so on. That is, each participant in the chain is both the initiator and endpoint of transmission of force for the same type of action – except the first in the chain, who is only an initiator, and the last, who is only an endpoint. Example: in The guests followed one another into the room, each guest is a follower and a 'followee', except the first and last in the chain. It is also possible to have a closed chain, as in people following each other in a circle, in which all participants are both initiator and endpoint. (Section 7.2)