Xy-pic

    A package for typesetting graphs and
   diagrams using TeX.  It is structured as several modules,
   each defining a custom notation for a particular kind of
   graphical object or structure.  Example objects are arrows,
   curves, and frames.  These can be organised in matrix,
   directed graph, path, polygon, knot, and 2-cell structure.

   Xy-pic works with LaTeX, AMS-LaTeX, AMS-TeX, and plain
   TeX, and has been used to typeset complicated diagrams from
   many application areas including category theory, automata
   theory, algebra, neural networks and database theory.

   <http://ens-lyon.fr/~krisrose/Xy-pic.html>.

   (1997-11-20)