/* 

  Robinson's Age in Picat.

  From Adrian Groza "Modelling Puzzles in First Order Logic"
  """
  Puzzle 9. Robinson’s age

  "How old are you, Robinson?” asked Colonel Crackham one morning. "Well, I forget
  exactly,” was the reply; "but my brother is two years older than me; my sister is four
  years older than him; my mother was twenty when I was born; and I was told yesterday
  that the average age of the four of us is thirty-nine years.” What was Robinson’s age?
  (puzzle 45 from Dudeney 2016)
  """  

  Unique solution:

  [robinson = 32,brother = 34,sister = 38,mother = 52]


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

*/

import cp.

main => go.

go ?=>
  [Robinson,Brother,Sister,Mother] :: 1..100,
  
  % "my brother is two years older than me;"
  Brother #= Robinson + 2,
  
  % "my sister is four years older than him;"
  Sister #= Brother + 4,
  
  % "my mother was twenty when I was born;"
  Mother #= Robinson + 20,
  
  % "and I was told yesterday that the average age of the four of us is thirty-nine years."
  4*39 #= Robinson + Brother + Sister + Mother,
  % 39 #= (Robinson + Brother + Sister + Mother) div 4, % Gives the same solution

  Vars = [robinson=Robinson,brother=Brother,sister=Sister,mother=Mother],
  solve(Vars),
  
  println(Vars),
  fail,
 
  nl.
go => true.