  A signed graph is a graph with a function that assigns a label of positive or
negative to each edge. The sign of a circle is the product of the signs of its
edges; a graph is balanced if all of its circles are positive. A set of edges
whose negation yields a balanced graph is a negation set. Results: tests to
determine whether a negation set is minimal, minimum, or the unique minimum;
any two disjoint negation sets must be bipartite; two classes of graphs are
shown to have bipartite negation sets (in general, existence is an unsolved
problem); I give an algorithm which finds a maximum family of disjoint negation
sets that includes a given negation set.
