latex code for connections in double groupoids

I have to develop in a hand-to-mouth way some code for connections and thin elements in a (edge-symmetric, to be precise) double groupoid, and for direction arrows. In case anyone wants to use this code I have put it on a web page www.bangor.ac.uk/r.brown/latexconn-code.html with one example of its use. It is used throughout the book on `Nonabelian algebraic topology'. Even better, if anyone can improve on this code and let me know, I would be very grateful! The aim has been to have heavier symbols than those such as \lrcorner, ... Ronnie Brown [For admin and other information see: http://www.mta.ca/~cat-dist/ ]