Graph union
Graph operations produce new graphs from initial ones. They may be separated into the following major categories.
Unary operations create a new graph from one initial one.
Elementary operations or editing operations create a new graph from one initial one by a simple local change, such as addition or deletion of a vertex or of an edge, merging and splitting of vertices, edge contraction, etc. The graph edit distance between a pair of graphs is the minimum number of elementary operations required to transform one graph into the other.
Advanced operations create a new graph from one initial one by a complex changes, such as:
Binary operations create a new graph from two initial ones G1 = (V1, E1) and G2 = (V2, E2), such as:
...
Wikipedia