Rotation map

In mathematics, a rotation map is a function that represents an undirected edge-labeled graph, where each vertex enumerates its outgoing neighbors. Rotation maps were first introduced by Reingold, Vadhan and Wigderson (“Entropy waves, the zig-zag graph product, and new constant-degree expanders”, 2002) in order to conveniently define the zig-zag product and prove its properties. Given a vertex ${\displaystyle v}$ and an edge label ${\displaystyle i}$, the rotation map returns the ${\displaystyle i}$'th neighbor of ${\displaystyle v}$ and the edge label that would lead back to ${\displaystyle v}$.