Infinite Sets
The pigeonhole principle can be extended to infinite sets by phrasing it in terms of cardinal numbers: if the cardinality of set A is greater than the cardinality of set B, then there is no injection from A to B. However in this form the principle is tautological, since the meaning of the statement that the cardinality of set A is greater than the cardinality of set B is exactly that there is no injective map from A to B. What makes the situation of finite sets interesting is that adding at least one element to a set is sufficient to ensure that the cardinality increases.
Read more about this topic: Pigeonhole Principle
Famous quotes containing the words infinite and/or sets:
“Since [man] is infinitely removed from comprehending the extremes, the end of things and their beginning are hopelessly hidden from him in an impenetrable secret; he is equally incapable of seeing the nothing from which he was made, and the infinite in which he is swallowed up.”
—Blaise Pascal (1623–1662)
“In the beautiful, man sets himself up as the standard of perfection; in select cases he worships himself in it.... Man believes that the world itself is filled with beauty—he forgets that it is he who has created it. He alone has bestowed beauty upon the world—alas! only a very human, an all too human, beauty.”
—Friedrich Nietzsche (1844–1900)