title: how to find neighbors for cell in akari by prolog
body: <p>I try to solve akari/light-up game in prolog .
  Firstly I want to find the four cells around a cell by neighbors() but it gives one cell only ... After that I want to find all cells in y with this cell by yneighbors() .... Anything as help will be useful .....
  my code :</p>
  
  <pre><code>size(8,8).
  
  wall(1,6).
  wall(2,2).
  wall(2,3).
  wall(3,7).
  wall(4,1).
  wall(4,5).
  wall(5,4).
  wall(5,8).
  wall(6,2).
  wall(7,6).
  wall(7,7).
  wall(8,3).
  
  wallnum(1,6,1).
  wallnum(2,2,3).
  wallnum(3,7,0).
  wallnum(5,4,4).
  wallnum(5,8,0).
  wallnum(6,2,2).
  wallnum(7,6,1).
  
  light(1,2).
  light(1,7).
  light(2,1).
  light(2,8).
  light(3,2).
  light(4,4).
  light(4,6).
  light(5,3).
  light(5,5).
  light(6,1).
  light(6,4).
  light(7,2).
  light(7,8).
  light(8,6).
  
  cell(X,Y):-X&gt;0,X&lt;9,Y&gt;0,Y&lt;9.
  
  neighbors(X,Y,L):-cell(X,Y),
  cell(X+1,Y),X1 is X + 1,Y1 is Y  ,L =[X1,Y1];
  cell(X-1,Y),X1 is X - 1,Y1 is Y  ,L=[X1,Y1];
  cell(X,Y+1),X1 is X    ,Y1 is Y + 1 ,L=[X1,Y1];
  cell(X,Y-1),X1 is X    ,Y1 is Y - 1 ,L=[X1,Y1].
  
  yneighbors(X,Y,L):-cell(X,Y+1),L=[X,Y].
  </code></pre>