many thanks, Charles, somehow I forgot that the Elephant is also about Sketches. I came across this recent paper by Diskin&Wolter http://www.cs.toronto.edu/~zdiskin/Pubs/ACCAT-07.pdf where the authors propose a version of sketch-based syntax for Computer Science purposes. The main idea here (as far as I understood the paper) is to use sketches as arities of predicates. I heard about similar ideas from Rene Guitart in private conversations (but Rene's approach is algebraic rather than logical). Looking at GBLS briefly I couldn't immediately grasp if your and Atish Bagchi's approach to graph-based logic is based on similar ideas or your approach is quite different. I certainly should read GBLS more carefully for discussing it but I would grateful for a hint. Andrei Selon Charles Wells <charles@abstractmath.org>:
I have not kept up with the field very well, but I can recommend these works:
Peter Johnstone, *Sketches of an Elephant*, Vol. 2, OUP 2003: the chapter on sketches. (I am in rural Wisconsin at the moment asnd don't have access to the book. If OUP would make its pages available to look at on Amazon I could have told you the exact page.)
Bagchi and Wells, *Graph Based Logic and Sketches*, here:
http://arxiv.org/PS_cache/arxiv/pdf/0809/0809.3023v1.pdf
Also Kinoshita, et al 1997, referred to in GBLS. There might be relevant papers since 1993 mentioned in the Elephant, too.
Category people: If you can suggest other papers that should be included, let me know soon, and I will revise the sketches paper to include them (and the ones I mentioned above).
Charles Wells