Assignment 1:
due by the end of class Wednesday January 17 2001.

On page 1, McHugh defines a graph as a set of vertices
together with a set of edges, where each edge
is an unordered pair of vertices.
It is clear from the discussion in paragraph 3 of page 4
that he means "pair of *distinct* vertices",
namely, that no edge of a graph is a loop.
Explain carefully why an alternate definition
of `graph' is `irreflexive symmetric binary relation',
and give a similar alternate definition of `digraph'.
 chapter 1, questions 1,2,3,4,5,6,7