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On the Erd\H{o}s-Tuza-Valtr Conjecture
The Erd\H{o}s-Szekeres conjecture states that any set of more than
points in the plane with no three on a line contains the vertices of a convex
-gon. Erd\H{o}s, Tuza, and Valtr strengthened the conjecture by stating that
any set of more than points in a
plane either contains the vertices of a convex -gon, points lying on a
concave downward curve, or points lying on a concave upward curve. They
also showed that the generalization is actually equivalent to the
Erd\H{o}s-Szekeres conjecture.
We prove the first new case of the Erd\H{o}s-Tuza-Valtr conjecture since the
original 1935 paper of Erd\H{o}s and Szekeres. Namely, we show that any set of
points in the plane with no three points on a line and no
two points sharing the same -coordinate either contains 4 points lying on a
concave downward curve or the vertices of a convex -gon.Comment: 16 pages, 8 figure