3
$\begingroup$

This question was asked several months ago on Math.SE, but remains unsolved.

For any collection of permutations of $\{1,2,\dots,n\}$, we say that it realizes a directed multigraph with $1,2,\dots,n$ as vertices, such that there is an edge from $i$ to $j$ if $i$ appears before $j$ in at least half of the permutations, and there is an extra edge from $i$ to $j$ (so, two edges in total) if $i$ appears before $j$ in all of the permutations.

Is it true that for any collection of permutations that realizes a multigraph $G$, there exists a collection of two permutations (not necessarily distinct, and not necessarily from the original collection) that realizes a multigraph $H$ such that the edge set of $H$ is a superset of the edge set of $G$?

For example, if we have a collection of permutations

$(1,2,3,4), (1,4,3,2), (2,3,1,4), (3,1,2,4)$

the graph $G$ contains two edges $(1,4)$ and one edge $(1,2), (1,3), (2,3), (2,4), (3,1), (3,2), (3,4)$ each. Then we can choose the collection

$(1,2,3,4), (3,1,2,4)$

to fulfill the condition, since the realized graph $H$ contains two edges $(1,2), (1,4), (2,4), (3,4)$ each and one edge $(1,3), (2,3), (3,1), (3,2)$ each.

$\endgroup$

0

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.