Q:

Doubt over a term in the definition

I was studying a book Handbook of Product Graphs by Richard Hammack, Wilfried  Imrich, Sandi Klavžar. There is a definition of Antipodal Graph.
A graph $G$ is called antipodal if there exists a vertex $v$ to any vertex $u$ $\in$ $V(G)$ such that  $V(G) = I(u,v)$.
What does $I(u,v)$ here stands for. 
What I know about the antipodal graph of a graph $G$ is that its a graph containing vertices of $G$ and those vertices are adjacent in antipodal graph whose distance equals diameter of $G$.
Thanks a lot for help.

A:

It’s defined near the top of page $9$, according to the Look Inside feature at Amazon: $I(u,v)$, the interval between $u$ and $v$, is the set of vertices lying on shortest paths between $u$ and $v$, including the vertices $u$ and $v$ themselves. For example, an even cycle $C_{2n}$ is antipodal, because if $u$ is any vertex, we may take $v$ to be the diametrically opposite vertex at distance $n$ from $u$, and $I(u,v)$ will then be the whole graph: the two paths from $u$ to $v$ are both of minimum length, and every vertex of $C_{2n}$ lies on one of them.

