Editing Graph minor (section)

===Shallow minors===
A [[shallow minor]] of a graph ''G'' is a minor in which the edges of ''G'' that were contracted to form the minor form a collection of disjoint subgraphs with low [[Diameter (graph theory)|diameter]]. Shallow minors interpolate between the theories of graph minors and subgraphs, in that shallow minors with high depth coincide with the usual type of graph minor, while the shallow minors with depth zero are exactly the subgraphs.<ref>{{harvtxt|Nešetřil|Ossona de Mendez|2012}}.</ref> They also allow the theory of graph minors to be extended to classes of graphs such as the [[1-planar graph]]s that are not closed under taking minors.<ref>{{harvtxt|Nešetřil|Ossona de Mendez|2012}}, pp. 319–321.</ref>