parid0048 | Sun, 19 Jan 2003 16:17:10
The first letter of an arc type's name is the name of one of its endpoint types. The second letter of the arc type's name is the name of its other endpoint type. That is, an AT arc has two endpoints, one of endpoint type "A" and the other of endpoint type "T".
Arc type names are built from the types of the endpoints of the arc. Thus, an AT arc, has an endpoint of type "A" and an endpoint of type "T."
The revision assumes "name of one of its endpoint types" but I think it is implied that a type has to have a name. I think the revision expresses the same rule as the original but a little more clearly.