/* 

  Global constraint equivalent in Picat.

  From Global Constraint Catalogue
  http://www.emn.fr/x-info/sdemasse/gccat/Cequivalent.html
  """
  Constraint

      equivalent(VAR,VARIABLES)

  Purpose

      Let VARIABLES be a collection of 0-1 variables VAR1,VAR2. Enforce VAR=(VAR1<=>VAR2).

  Example
      (1,<0,0>)
      (0,<0,1>)
      (0,<1,0>)
      (1,<1,1>)
  """


  This Picat model was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/

import cp.

main => go.

go ?=>
  B :: 0..1,
  Variables = new_list(2),
  Variables :: 0..1,

  equivalent(B, Variables),

  Vars = Variables ++ [B],
  solve(Vars),
  println(variables=Variables),
  println(b=B),  
  nl,
  fail,
  
  nl.

go => true.

equivalent(V, Vars) =>
   N = Vars.len,
   NumPairs = N*(N-1) div 2, % number of comparison
   sum([Vars[I] #= Vars[J]  : I in 1..N, J in I+1..N ]) #= NumPairs #<=> V #= 1.