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The 3-node tournament (and directed graph) illustrated above (Harary 1994, p. 205).

The set of all centroid points in a weighted tree (Harary 1994, p. 36).

Let a knot K be n-embeddable. Then its tunnel number is a knot invariant which is related to n.

If the Tutte polynomial T(x,y) of a graph G is given by sumt_(rs)x^ry^s, then the matrix (t_(rs)) is called the rank matrix of G. For example, the Tutte matrix of the ...

Let a cotree of a spanning tree T in a connected graph G be denoted T^*. Then the edges of G which are not in T^* are called its twigs (Harary 1994, p. 39).

Let graph G have p points v_i and graph H have p points u_i, where p>=3. Then if for each i, the subgraphs G_i=G-v_i and H_i=H-u_i are isomorphic, then the graphs G and H are ...

An R-module M is said to be unital if R is a commutative ring with multiplicative identity 1=1_R and if 1m=m for all elements m in M.

An aliquot sequence computed using the analog of the restricted divisor function s^*(n) in which only unitary divisors are included.

Sociable numbers computed using the analog of the restricted divisor function s^*(n) in which only unitary divisors are included.

A weakly connected component of a simple directed graph (i.e., a digraph without loops) is a maximal subdigraph such that for every pair of distinct vertices u, v in the ...