This is just to let everyone know that I've just completed a 50-page PDF on "Exact Echoes"
This is based on the Exact Echoes tourney held in Chessics in 1983-5.
Sorry it's taken me 25 years to get round to completing it!
Since this booklet covers all types of stipulations I wasn't sure where to mention it here.
The mathematics comes in to describing the different transformations possible:
identity, translation, rotation, reflection and the lesser known transflection,
which is a reflection in a line combined with a translation along the line.