olymmath

Putnam 1996 A4

  • Session A

Let SS be the set of ordered triples (a,b,c)(a, b, c) of distinct elements of a finite set AA. Suppose that

  1. (a,b,c)∈S(a,b,c) \in S if and only if (b,c,a)∈S(b,c,a) \in S;

  2. (a,b,c)∈S(a,b,c) \in S if and only if (c,b,a)∉S(c,b,a) \notin S;

  3. (a,b,c)(a,b,c) and (c,d,a)(c,d,a) are both in SS if and only if (b,c,d)(b,c,d) and (d,a,b)(d,a,b) are both in SS.

Prove that there exists a one-to-one function gg from AA to RR such that g(a)<g(b)<g(c)g(a) < g(b) < g(c) implies (a,b,c)∈S(a,b,c) \in S. Note: RR is the set of real numbers.

Curated text Kedlaya Putnam archive. Quoted with source.

Solutions

Human solution Solution 1 by Manjul Bhargava and Kiran Kedlaya

The terms of the source let olymmath link to this solution but not copy it. Read the solution (Kedlaya Putnam archive).

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