Double Cover

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:

    “...the shiny-cheeked merchant bankers from London with eighties striped blue ties and white collars and double-barreled names and double chins and double-breasted suits, who said “ears” when they meant “yes” and “hice” when they meant “house” and “school” when they meant “Eton”...”
    —John le Carré (b. 1931)

    “Every individual ought to know at least one poet from cover to cover: if not as a guide through the world, then as a yardstick for the language.”
    —Joseph Brodsky (b. 1940)