4 From Networks to Automata
  
  It  is  known  that  the  language  of  all encoded permutations of a TPN is
  rational,  and  thus  is it indeed possible to turn a TPN into an automaton.
  The  idea  is  to inspect all dispositions of tokens within the TPN and find
  equivalence  classes  of  these  dispositions, for more details consult [3].
  Adding  a  constraint,  which limits the number of tokens at any time within
  the TPN, is also considered in this chapter.
  
  The  algorithms  featured in this chapter do not return the minimal automata
  representing  the  input TPN as they are exactly visualising the equivalence
  classes  of  the dispositions of the tokens in the TPN. The automaton can be
  minimalised  by  choice,  as it simplifies future computations involving the
  automaton also is makes the automata more legible.
  
  
  4.1 Functions
  
  4.1-1 GraphToAut
  
  GraphToAut( g, innode, outnode )  function
  Returns:  An automaton representing the input TPN.
  
  GraphToAut  turns an array represented directed graph, with a distinct input
  node  and  a  distinct  output  node, into the corresponding automaton, that
  accepts the language build by the resulting rank encoded permutations of the
  directed graph.
  
    Example  
    gap> x:=Seqstacks(2,2);
    [ [ 2 ], [ 3, 4 ], [ 2 ], [ 5, 6 ], [ 4 ], [  ] ]
    gap> aut:=GraphToAut(x,1,6);
    < epsilon automaton on 4 letters with 64 states >
    gap> aut:=MinimalAutomaton(aut);
    < deterministic automaton on 3 letters with 3 states >
    gap> Display(aut);
       |  1  2  3  
    --------------
     a |  1  3  1  
     b |  3  3  3  
     c |  2  2  2  
    Initial state:   [ 1 ]
    Accepting state: [ 1 ]
    gap> 
  
  
    Example  
    gap> x:=Parstacks(2,2);
    [ [ 2, 4 ], [ 3, 6 ], [ 2 ], [ 5, 6 ], [ 4 ], [  ] ]
    gap> aut:=GraphToAut(x,1,6);
    < epsilon automaton on 5 letters with 66 states >
    gap> aut:=MinimalAutomaton(aut);
    < deterministic automaton on 4 letters with 9 states >
    gap> Display(aut);
       |  1  2  3  4  5  6  7  8  9  
    --------------------------------
     a |  1  2  1  3  2  2  6  6  3  
     b |  3  2  3  3  4  3  6  9  3  
     c |  9  2  9  4  6  6  4  9  9  
     d |  8  2  8  7  5  5  7  8  8  
    Initial state:   [ 1 ]
    Accepting state: [ 1 ]
    gap> 
  
  
    Example  
    gap> x:=BufferAndStack(3,2);
    [ [ 2 .. 4 ], [ 5 ], [ 5 ], [ 5 ], [ 6, 7 ], [ 5 ], [  ] ]
    gap> aut:=GraphToAut(x,1,7);
    < epsilon automaton on 5 letters with 460 states >
    gap> aut:=MinimalAutomaton(aut);
    < deterministic automaton on 4 letters with 4 states >
    gap> Display(aut);
       |  1  2  3  4  
    -----------------
     a |  1  4  1  3  
     b |  3  4  3  3  
     c |  4  4  4  4  
     d |  2  2  2  2  
    Initial state:   [ 1 ]
    Accepting state: [ 1 ]
    gap> 
  
  
    Example  
    gap> x:=[[2,3],[4],[5],[3,6],[6],[]];
    [ [ 2, 3 ], [ 4 ], [ 5 ], [ 3, 6 ], [ 6 ], [  ] ]
    gap> aut:=GraphToAut(x,1,6);
    < epsilon automaton on 4 letters with 80 states >
    gap> aut:=MinimalAutomaton(aut);
    < deterministic automaton on 3 letters with 8 states >
    gap> Display(aut);
       |  1  2  3  4  5  6  7  8  
    -----------------------------
     a |  1  3  1  4  6  1  6  1  
     b |  3  8  3  4  4  6  6  6  
     c |  2  2  2  4  5  5  7  7  
    Initial state:   [ 1 ]
    Accepting state: [ 1 ]
    gap> 
  
  
  The input TPN here is the first network described in Chapter 2..
  
  4.1-2 ConstrainedGraphToAut
  
  ConstrainedGraphToAut( g, innode, outnode, capacity )  function
  Returns:  An automaton representing the input TPN with bounded capacity.
  
  ConstrainedGraphToAut  builds an epsilon automaton based on the same idea as
  GraphToAut,  so  it  takes  a  list  representation  of  a directed graph, a
  designated  input node and a distinct output node, but additionally there is
  the  constraint  that  there can be at most capacity tokens in the graph, at
  any time.
  
    Example  
    gap> x:=Seqstacks(2,2);                  
    [ [ 2 ], [ 3, 4 ], [ 2 ], [ 5, 6 ], [ 4 ], [  ] ]
    gap> aut:=ConstrainedGraphToAut(x,1,6,2);
    < epsilon automaton on 6 letters with 21 states >
    gap> aut:=MinimalAutomaton(aut);         
    < deterministic automaton on 5 letters with 3 states >
    gap> Display(aut);                       
       |  1  2  3  
    --------------
     a |  1  2  1  
     b |  3  2  3  
     c |  2  2  2  
     d |  2  2  2  
     e |  2  2  2  
    Initial state:   [ 1 ]
    Accepting state: [ 1 ]
    gap> 
  
  
    Example  
    gap> x:=BufferAndStack(3,2);      
    [ [ 2 .. 4 ], [ 5 ], [ 5 ], [ 5 ], [ 6, 7 ], [ 5 ], [  ] ]
    gap> aut:=ConstrainedGraphToAut(x,1,6,3);
    < epsilon automaton on 7 letters with 112 states >
    gap> aut:=MinimalAutomaton(aut);
    < deterministic automaton on 6 letters with 4 states >
    gap> Display(aut);
       |  1  2  3  4  
    -----------------
     a |  1  2  1  3  
     b |  3  2  3  3  
     c |  4  2  4  4  
     d |  2  2  2  2  
     e |  2  2  2  2  
     f |  2  2  2  2  
    Initial state:   [ 1 ]
    Accepting state: [ 1 ]
    gap> 
  
  
    Example  
    gap> x:=[[2,3],[4],[5],[3,6],[6],[]];                      
    [ [ 2, 3 ], [ 4 ], [ 5 ], [ 3, 6 ], [ 6 ], [  ] ]
    gap> aut:=ConstrainedGraphToAut(x,1,6,3);
    < epsilon automaton on 6 letters with 48 states >
    gap> aut:=MinimalAutomaton(aut);         
    < deterministic automaton on 5 letters with 8 states >
    gap> Display(aut);                       
       |  1  2  3  4  5  6  7  8  
    -----------------------------
     a |  1  3  1  4  6  1  6  1  
     b |  3  8  3  4  4  6  6  6  
     c |  2  2  2  4  5  5  7  7  
     d |  4  4  4  4  4  4  4  4  
     e |  4  4  4  4  4  4  4  4  
    Initial state:   [ 1 ]
    Accepting state: [ 1 ]
    gap>