8. Drawing automata
  
  The  drawing  of  graphs  described  here  uses   graphviz  , a software for
  drawing  graphs  developed  at  AT  &  T  Labs,  that  can  be  obtained at 
  http://www.research.att.com/sw/tools/graphviz/  .
  
  
  8.1 Installing some external programs
  
  If  you  work  under    LINUX   , you should install graphviz and create the
  directory  ~ /dot-tmp  .
  
  
  8.2 Functions to draw automata
  
  8.2-1 DrawAutomaton
  
  > DrawAutomaton( A[, file] ) _______________________________________function
  
  This  function  draws  automaton    A    writing  the  needed data in file ~
  /dot-tmp/file.
  
  8.2-2 DrawAutomata
  
  > DrawAutomata( A, B[, file] ) _____________________________________function
  
  This  function tests if automaton  A  is a subautomaton of  B  in which case
  draws    B    highlighting  the edges not in  A  by drawing them in a dotted
  style,  while  the  others  are drawn in a plain style and writes the needed
  data in file ~ /dot-tmp/file.
  
  8.2-3 DrawGraph
  
  > DrawGraph( G[, file] ) ___________________________________________function
  
  Draws  a graph specified as an adjacency list  G  and writes the needed data
  in file ~ /dot-tmp/file.
  
  8.2-4 DrawSCCAutomaton
  
  > DrawSCCAutomaton( A[, file] ) ____________________________________function
  
  Draws  automaton    A   and highlights it's strongly connected components by
  drawing  their  edges  in  a  dotted  style  and their vertices in a lighter
  colour. Writes the needed data in file ~ /dot-tmp/file.