ljdickey@watmath.UUCP (06/10/83)
OK, Dean Hoffman has solved your puzzle.
Here are two graphs, each with 9 vertices.
That means there are 36 pairs of vertices.
Each of them has 12 pairs with distance 2 apart, and
each of them has 24 pairs with distance 4 apart.
o o o o
| \|/
o o--o--o
| |
o--o------o------o--o o--o------o------o--o
/|\ /|\ | |
o o o o o o o o
Lee Dickey
Department of Pure Mathematics
University of Waterloo
...!decvax!watmath!ljdickey