  An equiangular tight frame (ETF) is a set of unit vectors whose coherence
achieves the Welch bound, and so is as incoherent as possible. They arise in
numerous applications. It is well known that real ETFs are equivalent to a
certain subclass of strongly regular graphs. In this note, we give some
alternative techniques for understanding this equivalence. In a later document,
we will use these techniques to further generalize this theory.
