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:
“In a symbol there is concealment and yet revelation: here therefore, by silence and by speech acting together, comes a double significance.... In the symbol proper, what we can call a symbol, there is ever, more or less distinctly and directly, some embodiment and revelation of the Infinite; the Infinite is made to blend itself with the Finite, to stand visible, and as it were, attainable there. By symbols, accordingly, is man guided and commanded, made happy, made wretched.”
—Thomas Carlyle (1795–1881)
“Every man alone is sincere. At the entrance of a second person, hypocrisy begins. We parry and fend the approach of our fellow-man by compliments, by gossip, by amusements, by affairs. We cover up our thought from him under a hundred folds.”
—Ralph Waldo Emerson (1803–1882)