MathDB
Exists c such that f(c) = c

Source: IMC 2007 Day 2 Problem 3

August 7, 2007
functionlimitPutnamIMCcollege contests

Problem Statement

Let C C be a nonempty closed bounded subset of the real line and f:CC f: C\to C be a nondecreasing continuous function. Show that there exists a point pC p\in C such that f(p) \equal{} p. (A set is closed if its complement is a union of open intervals. A function g g is nondecreasing if g(x)g(y) g(x)\le g(y) for all xy x\le y.)