anchor.diff:  
   
   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  -% PropEr predicates
  +%% PropEr predicates
   %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
   
   %% -include_lib("proper/include/proper.hrl").
  
positive.code:     solve({12,12,{11,5}}, [{0,{{1,5},y,3}}, {1,{{0,5},x,7}}, {2,{{5,3},x,4}}, {3,{{3,2},y,3}}, {4,{{2,1},x,4}}, {5,{{1,0},y,2}}, {6,{{3,7},x,3}}, {7,{{4,8},y,4}}, {8,{{8,7},x,4}}, {9,{{7,0},x,5}}, {10,{{8,4},y,4}}, {11,{{1,10},y,4}}, {12,{{5,9},x,3}}, {13,{{7,11},y,4}}, {14,{{9,5},x,6}}], Opts).
  
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  % Input/Output
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  
  -spec print(room(), state()) -> _.
  print(Room, Cars) ->
      print({0,-1}, Room, Cars).
  
  -spec print({0..1 | length(),-1..1 | length()}, room(), state()) -> _.
  print({_X,_Height}, {_Width,_Height,_Exit}, _Cars) ->
      io:format("~n", []);
  print({Width,Y}, {Width,Height,Exit}, Cars) ->
  
negative.code: 	    end;
  	[{Num,_Coords}] ->
  	    io:format("~2b", [Num])
  	    %% TODO: allow more digits
      end,
      print({X + 1,Y}, Room, Cars).
  
  