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Let $e = \lbrace u,v\rbrace$, $e' = \lbrace v,u'\rbrace$ be edges of an undirected graph $G$ and $ee'$ be the path from $u$ through $v$ to $u'$. The following defintions make sense for every graph and thus are purely combinatorial:

Definition 1: $ee'$ is a pre-geodesic when it is the unique shortest path between $u$ and $u'$

Definition 2: A pre-geodesic $ee'$ is a geodesic when there is no other edge $f$ through $v$ such that $ef$ or $e'f$ is a pre-geodesic.

The first condition is motivated by the fact that geodesics in differential geometry are locally shortest paths and as such locally unique. It prevents the graph

from having geodesics.

The second condition reflects the fact, that geodesics usually do not “split”. It prevents the graph

from having geodesics.

But now, let's restrict to polyhedral graphs. I wonder if it's true for polyhedral graphs that only a small number of patterns of geodesics going through a given vertex $v$ are possible:

• Which patterns?

• How to prove this?

Have a look at this gallery of vertices $v$ (grey, drawn with all their neighbours) with degree at most 6 and at most three geodesics (red, blue, green) passing through them (all the other vertices may or must have further neighbours):

• Is this gallery essentially complete?

• If so: how to prove it?

Otherwise:

• Is there a polyhedral graph with a vertex of degree 7 with a geodesic passing through it?

• Is there a polyhedral graph with a vertex with four geodesics passing through it?

4 added 151 characters in body

Let $e = \lbrace u,v\rbrace$, $e' = \lbrace v,u'\rbrace$ be edges of an undirected graph $G$ and $ee'$ be the path from $u$ through $v$ to $u'$. The following defintions make sense for every graph and thus are purely combinatorial:

Definition 1: $ee'$ is a pre-geodesic when it is the unique shortest path between $u$ and $u'$

Definition 2: A pre-geodesic $ee'$ is a geodesic when there is no other edge $f$ through $v$ such that $ef$ or $e'f$ is a pre-geodesic.

The first condition is motivated by the fact that geodesics in differential geometry are locally shortest paths and as such locally unique. It prevents the graph

from having geodesics.

The second condition reflects the fact, that geodesics usually do not “split”. It prevents the graph

from having geodesics.

But now, let's restrict to polyhedral graphs. I wonder if it's true for polyhedral graphs that only a small number of patterns of geodesics going through a given vertex $v$ are possible:

1. Which patterns?
2. How to prove this?

Have a look at this gallery of vertices $v$ (grey, drawn with all their neighbours) with degree at most 6 and at most three geodesics (red, blue, green) passing through them (all the other vertices may or must have further neighbours):

Is this gallery essentially complete?

If so: how to prove it?

Otherwise: are

• Is there - for example - a polyhedral graphs graph with a vertex of degree 7 with a geodesic passing through it?

• Is there a polyhedral graph with a vertex with four geodesics passing through one vertexit?

3 edited body

Let $e = \lbrace u,v\rbrace$, $e' = \lbrace v,u'\rbrace$ be edges of an undirected graph $G$ and $ee'$ be the path from $u$ through $v$ to $u'$. The following defintions make sense for every graph and thus are purely combinatorial:

Definition 1: $ee'$ is a pre-geodesic when it is the unique shortest path between $u$ and $u'$

Definition 2: A pre-geodesic $ee'$ is a geodesic when there is no other edge $f$ through $v$ such that $ef$ or $e'f$ is a pre-geodesic.

The first condition is motivated by the fact that geodesics in differential geometry are locally shortest paths and as such locally unique. It prevents the graph

from having geodesics.

The second condition reflects the fact, that geodesics usually do not “split”. It prevents the graph

from having geodesics.

But now, let's restrict to polyhedral graphs. I wonder if it's true for polyhedral graphs that only a small number of patterns of geodesics going through a given vertex $v$ are possible:

1. Which patterns?
2. How to prove this?

Have a look at this gallery of vertices $v$ (grey, drawn with all their neighbours) with at most three geodesics passing through them (all the other vertices may or must have further neighbours):

Is this gallery complete?

If so: how to prove it?

Otherwise: are there - for example - polyhedral graphs with four geodesics passing through one vertex?

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