# Nowhere-zero flows

Open problems about Nowhere-zero flows (not to be confused with Network flows).

## Jaeger's modular orientation conjecture ★★★

Author(s): Jaeger

**Conjecture**Every -edge-connected graph can be oriented so that (mod ) for every vertex .

Keywords: nowhere-zero flow; orientation

## Bouchet's 6-flow conjecture ★★★

Author(s): Bouchet

**Conjecture**Every bidirected graph with a nowhere-zero -flow for some , has a nowhere-zero -flow.

Keywords: bidirected graph; nowhere-zero flow

## The three 4-flows conjecture ★★

Author(s): DeVos

**Conjecture**For every graph with no bridge, there exist three disjoint sets with so that has a nowhere-zero 4-flow for .

Keywords: nowhere-zero flow

## A homomorphism problem for flows ★★

Author(s): DeVos

**Conjecture**Let be abelian groups and let and satisfy and . If there is a homomorphism from to , then every graph with a B-flow has a B'-flow.

Keywords: homomorphism; nowhere-zero flow; tension

## Real roots of the flow polynomial ★★

Author(s): Welsh

**Conjecture**All real roots of nonzero flow polynomials are at most 4.

Keywords: flow polynomial; nowhere-zero flow

## Unit vector flows ★★

Author(s): Jain

**Conjecture**For every graph without a bridge, there is a flow .

**Conjecture**There exists a map so that antipodal points of receive opposite values, and so that any three points which are equidistant on a great circle have values which sum to zero.

Keywords: nowhere-zero flow

## Antichains in the cycle continuous order ★★

Author(s): DeVos

If , are graphs, a function is called *cycle-continuous* if the pre-image of every element of the (binary) cycle space of is a member of the cycle space of .

**Problem**Does there exist an infinite set of graphs so that there is no cycle continuous mapping between and whenever ?

## Circular flow number of regular class 1 graphs ★★

Author(s): Steffen

A nowhere-zero -flow on is an orientation of together with a function from the edge set of into the real numbers such that , for all , and . The circular flow number of is inf has a nowhere-zero -flow , and it is denoted by .

A graph with maximum vertex degree is a class 1 graph if its edge chromatic number is .

**Conjecture**Let be an integer and a -regular graph. If is a class 1 graph, then .