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:

    “Go; and if that word have not quite killed thee,
    Ease me with death by bidding me got too.
    Oh, if it have, let my word work on me,
    And a just office on a murderer do.
    Except it be too late to kill me so,
    Being double dead: going, and bidding go.”
    —John Donne (1572–1631)

    “Again we have here two distinctions that are no distinctions, but made to seem so by terms invented by I know not whom to cover ignorance, and blind the understanding of the reader: for it cannot be conceived that there is any liberty greater, than for a man to do what he will.”
    —Thomas Hobbes (1579–1688)