Quasigroups were originally described combinatorially, in terms of existence and uniqueness conditions on the solutions to certain equations. Evans introduced a universal-algebraic characterization, as algebras with three binary operations satisfying four identities. Now, quasigroups are redefined as heterogeneous algebras, satisfying just two conditions respectively known as hypercommutativity and hypercancellativity.
Hovey introduced A-cordial labelings in [4] as a simultaneous generalization of cordial and harmonious labelings. If A is an abelian group, then a labeling f: V(G) → A of the vertices of some graph G induces an edge-labeling on G; the edge uv receives the label f(u) + f(v). A graph G is A-cordial if there is a vertex-labeling such that (1) the vertex label classes differ in size by at most one and (2) the induced edge label classes differ in size by at most one. Research on A-cordiality has focused on the case where A is cyclic. In this paper, we investigate V₄-cordiality of many families of graphs, namely complete bipartite graphs, paths, cycles, ladders, prisms, and hypercubes. We find that all complete bipartite graphs are V₄-cordial except K_{m,n} where m,n ≡ 2(mod 4). All paths are V₄-cordial except P₄ and P₅. All cycles are V₄-cordial except C₄, C₅, and Cₖ, where k ≡ 2(mod 4). All ladders P₂ ☐ Pₖ are V₄-cordial except C₄. All prisms are V₄-cordial except P₂ ☐ Cₖ, where k ≡ 2(mod 4). All hypercubes are V₄-cordial, except C₄. Finally, we introduce a generalization of A-cordiality involving digraphs and quasigroups, and we show that there are infinitely many Q-cordial digraphs for every quasigroup Q.
This paper presents some manner of characterization of Boolean rings. These algebraic systems one can also characterize by means of some distributivities satisfied in GBbi-QRs.
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