Axiom:Symmetry of Betweenness

Axiom
Let $a$ and $b$ be points.

Let $\mathsf{B}$ be the relation of betweenness.


 * $\forall a,b: \mathsf{B}abc \implies \mathsf{B}cba$

Intuition
If a point is on a line segment, it's still on the line segment if you measure it from the other direction.