Art of Problem Solving
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2020 OIM Problems/Problem 3: Difference between revisions

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An "''operation''" consists of choosing two elements <math>a_k</math> and <math>a_l</math> of a sequence, with <math>k \ne l</math>,
An "''operation''" consists of choosing two elements <math>a_k</math> and <math>a_l</math> of a sequence, with <math>k \ne l</math>,
and replace <math>a_l</math> with <math>a'_l</math>  Show that, given a collection of <math>2^n-1</math> ''Limeñan'' sequences, each formed by <math>n</math> integers numbers, there are two of them, say <math>\beta</math> and <math>\gamma</math>, such that it is possible to transform <math>\beta</math> into <math>\gamma</math> by a finite number of operations.
and replace <math>a_l</math> with <math>a'_l</math>  Show that, given a collection of <math>2^n-1</math> ''Limeñan'' sequences, each formed by <math>n</math> integers numbers, there are two of them, say <math>\beta</math> and <math>\gamma</math>, such that it is possible to transform <math>\beta</math> into <math>\gamma</math> by a finite number of operations.
''''Clarification:'''' If all the elements of a sequence are equal, then that sequence is not ''Limeña''.
'''Clarification:''' If all the elements of a sequence are equal, then that sequence is not ''Limeña''.


~translated into English by Tomas Diaz. ~orders@tomasdiaz.com
~translated into English by Tomas Diaz. ~orders@tomasdiaz.com

Latest revision as of 08:38, 23 December 2023

Problem

Let $n \ge 2$ be an integer. A sequence $\alpha = (a_1, a_2, \cdots , a_n)$ of $n$ integers is "Limeña" (from Lima, Perú) if

\[gcd \left\{  a_i - a_j | a_i > a_j, 1 \le i, j \le n\right\} = 1\]

An "operation" consists of choosing two elements $a_k$ and $a_l$ of a sequence, with $k \ne l$, and replace $a_l$ with $a'_l$ Show that, given a collection of $2^n-1$ Limeñan sequences, each formed by $n$ integers numbers, there are two of them, say $\beta$ and $\gamma$, such that it is possible to transform $\beta$ into $\gamma$ by a finite number of operations. Clarification: If all the elements of a sequence are equal, then that sequence is not Limeña.

~translated into English by Tomas Diaz. ~orders@tomasdiaz.com

Solution

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See also

OIM Problems and Solutions