Changed "connectedness" to relationship. Have not reached even tenative conclusions about 3.3.3
and the "eight-fold" way, but suspect that mirror cases need not be enumerated explicitly.
The relationship (read arc) specifies a symmetric relationship between the two nodes. In other words,
specify the four arc types and note that the relationships represented by the arcs are symmetric.
Can enumerate all the combinations if that is seen as helpful in explanation but that could be
tossed into a note or something.