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Function defined on the set of all positive integers

Source: IMO ShortList 1988, Problem 19, Mexico 1, Problem 49 of ILL

November 3, 2005
functionalgebrafunctional equationIMO Shortlist

Problem Statement

Let f(n) f(n) be a function defined on the set of all positive integers and having its values in the same set. Suppose that f(f(n) \plus{} f(m)) \equal{} m \plus{} n for all positive integers n,m. n,m. Find the possible value for f(1988). f(1988).
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