In mathematics, a double cover or double covering may refer to:
- Double cover (topology), a two-to-one mapping from one topological space to another. Frequently occurring special cases include
- The orientable double cover of a non-orientable manifold.
- The bipartite double cover of an undirected graph G, formed by the graph tensor product G ×K2.
- A double covering group of a topological group such as a Lie group, a group extension of index two formed by a topological double cover. A double cover may also be used to refer to non-topological group extensions of index two, for instance extensions of finite groups.
- Cycle double cover, a collection of cycles in a graph that together include each edge twice. The cycle double cover conjecture is the unproven assertion that every bridgeless graph has a cycle double cover.
Double coverage may also refer to:
- Double coverage, a defensive strategy in American football, basketball, and other sports
- Being covered by more than one health insurance plan
Famous quotes containing the words double and/or cover:
“One key, one solution to the mysteries of the human condition, one solution to the old knots of fate, freedom, and foreknowledge, exists, the propounding, namely, of the double consciousness. A man must ride alternately on the horses of his private and public nature, as the equestrians in the circus throw themselves nimbly from horse to horse, or plant one foot on the back of one, and the other foot on the back of the other.”
—Ralph Waldo Emerson (1803–1882)
“There is reason in the distinction of civil and uncivil. The manners are sometimes so rough a rind that we doubt whether they cover any core or sap-wood at all.”
—Henry David Thoreau (1817–1862)