Common graph
In graph theory, an area of mathematics, common graphs belong to a branch of extremal graph theory concerning inequalities in homomorphism densities. Roughly speaking, F {\displaystyle F} is a common graph if it "commonly" appears as a subgraph, in a sense that the total number of copies of F {\displaystyle F} in any graph G {\displaystyle G} and its complement G ¯ {\displaystyle {\overline {G}}} is a large fraction of all possible copies of F {\displaystyle F} on the same vertices.