Ramsey's Theorem
For every coloring of the k-subsets of
a sufficiently large set X, there is an
s-element subsets of X whose k-subsets all have the same color.
Briefly, it says if a set is large enough, it must contain the structure you want.
Philosophically, it means that completely disorder is impossible when the set is large enough.
Application
How many terminals do we need in order to build a network with certain sub- networks ?
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