It seems to be an extract from "Foundations of Field Computation" by Bruce MacLennan, if you want to read the whole thing: http://web.eecs.utk.edu/~bmaclenn/FFC.pdf
He and Dr. Marcolli have a bunch of interesting stuff on their websites if you like this sort of stuff.
He and Dr. Marcolli have a bunch of interesting stuff on their websites if you like this sort of stuff.