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  2. Handshaking lemma - Wikipedia

    en.wikipedia.org/wiki/Handshaking_lemma

    The same proof can be interpreted as summing the entries of the incidence matrix of the graph in two ways, by rows to get the sum of degrees and by columns to get twice the number of edges. [5] For graphs, the handshaking lemma follows as a corollary of the degree sum formula. [8]

  3. Double counting (proof technique) - Wikipedia

    en.wikipedia.org/wiki/Double_counting_(proof...

    In more colloquial terms, in a party of people some of whom shake hands, an even number of people must have shaken an odd number of other people's hands; for this reason, the result is known as the handshaking lemma. To prove this by double counting, let () be the degree of vertex . The number of vertex-edge incidences in the graph may be ...

  4. Degree (graph theory) - Wikipedia

    en.wikipedia.org/wiki/Degree_(graph_theory)

    The formula implies that in any undirected graph, the number of vertices with odd degree is even. This statement (as well as the degree sum formula) is known as the handshaking lemma. The latter name comes from a popular mathematical problem, which is to prove that in any group of people, the number of people who have shaken hands with an odd ...

  5. Erdős–Gallai theorem - Wikipedia

    en.wikipedia.org/wiki/Erdős–Gallai_theorem

    The Erdős–Gallai theorem is a result in graph theory, a branch of combinatorial mathematics.It provides one of two known approaches to solving the graph realization problem, i.e. it gives a necessary and sufficient condition for a finite sequence of natural numbers to be the degree sequence of a simple graph.

  6. Mountain climbing problem - Wikipedia

    en.wikipedia.org/wiki/Mountain_climbing_problem

    A trivial example. In mathematics, the mountain climbing problem is a mathematical problem that considers a two-dimensional mountain range (represented as a continuous function), and asks whether it is possible for two mountain climbers starting at sea level on the left and right sides of the mountain to meet at the summit, while maintaining equal altitudes at all times.

  7. Liberals accuse elderly husband of US senator of snubbing ...

    www.aol.com/news/liberals-accuse-elderly-husband...

    During Sen. Fischer’s swearing-in ceremony last Friday, Harris, 60, shook the senator’s hand, thanked her for her work and then extended a handshake toward her husband, Bruce, and said ...

  8. Hockey-stick identity - Wikipedia

    en.wikipedia.org/wiki/Hockey-stick_identity

    Pascal's triangle, rows 0 through 7. The hockey stick identity confirms, for example: for n=6, r=2: 1+3+6+10+15=35.. In combinatorics, the hockey-stick identity, [1] Christmas stocking identity, [2] boomerang identity, Fermat's identity or Chu's Theorem, [3] states that if are integers, then

  9. Psychologists break down the meaning of Donald Trump's handshake

    www.aol.com/news/2017-05-30-psychologists-break...

    The way the president shakes hands has been in the news as of late, especially those with French President Emmanuel Macron. Macron said his first shake with Trump was a "moment of truth." Another ...