A simple, undirected graph is vertex-transitive if for any pair of vertices $x,y$, there exists an automorphism (adjacency-preserving self-bijection) $\phi$ such that $\phi(x)=y$.

What if, instead of **taking** $x$ to $y$ as above, we require the automorphism $\phi$ to **exchange** $x$ and $y$, i.e. $\phi(x)=y$ and $\phi(y)=x$?

- Is there a name for this natural refinement of the notion of vertex-transitivity?
- What is a simple example of a vertex-transitive graph which does not satisfy this?

Note that any Cayley graph whose generating set is conjugacy-invariant does satisfy this exchange property (take $\phi(u)=xu^{-1}y$).