====== Acyclic path ======
{{tag>graphs operators}}
===== Description =====
Finding an acyclic path, Path, from A to Z in Graph.


**Source**:  PROLOG programming for artificial intelligence, 3rd Edition, Harlow, 2001, ISBN 0-201-40375-7.

===== Download =====
Program source code: {{prolog:pllib:acyclic_path.pl}}

===== Listing =====
<code prolog>
% Figure 9.20  Finding an acyclic path, Path, from A to Z in Graph.





% path( A, Z, Graph, Path): Path is an acyclic path from A to Z in Graph



:- op( 900, fy, not).



path( A, Z, Graph, Path)  :-

  path1( A, [Z], Graph, Path).



path1( A, [A | Path1], _, [A | Path1] ).



path1( A, [Y | Path1], Graph, Path)  :-

  adjacent( X, Y, Graph),

  not member( X, Path1),                        % No-cycle condition

  path1( A, [X, Y | Path1], Graph, Path).

  

not Goal  :-

  Goal, !, fail

  ; 

  true.

</code>
===== Comments =====