anchor.diff:  #! Lastly, a method of displaying the Sudoku board from the names of the variables which are in the solution set.
   
   #! @ExampleSession
  -#! gap> ExampleFuncNamesToIndex := function( vari_names, var_included )
  +#! gap> ExampleFuncNamesToIndex := function( var_names, var_included )
   #! >      local vars, ind;
   #! >      vars := ListWithIdenticalEntries( Size( var_names ), 0 );
   #! >      ind := List( var_included, t -> Position( var_names, t ));
   #! >      vars{ ind }:=ListWithIdenticalEntries( Size( var_included ), 1 );
   #! >      return vars;
   #! > end;
  -#! function( vari_names, var_included ) ... end
  -#! gap> 
  -#! ExampleFuncIndexToNames := function( var_names, index_set )
  -#! >   return Filtered( var_names, t -> index_set[Position( var_names, t )] = 1. );
  +#! function( var_names, var_included ) ... end
  +#! gap> ExampleFuncIndexToNames := function( var_names, index_set )
  +#! >      local i, keep;
  +#! >      keep := [];
  +#! >      for i in var_names do
  +#! >         if index_set[Position( var_names, i)] = 1. then
  +#! >            Add(keep, i);
  +#! >         fi;
  +#! >      od;
  +#! >      return keep;
  +#
  +#	This line has been replaced with a for loop, since in GAP there is a bug wich doesn't like
  +#	the function inside Filtered. It gives a syntax warning, which then ruins the test command.
  +#	This should be fixed in a future version of GAP, and then the Filtered code can be used again.
  +#
  +# >   return Filtered( var_names, t -> index_set[Position( var_names, t )] = 1. );
   #! > end;
   #! function( var_names, index_set ) ... end
   #! gap> 
  
positive.code: #! 2
  #! gap> sol := GurobiSolution(model2);;
  #! gap> sol2 := ExampleFuncIndexToNames(var_names2, sol);;
  #! ExampleFuncDisplaySudoku( sol2 );
  #! [ [  8,  4,  2,  5,  9,  1,  7,  3,  6 ],
  #!   [  9,  3,  1,  6,  2,  7,  5,  4,  8 ],
  #!   [  5,  6,  7,  8,  3,  4,  9,  1,  2 ],
  
negative.code: #! true
  #! gap> GurobiOptimiseModel( model3 );
  #! 2
  #! gap> number_of_solutions := 0;;
  #! gap> while GurobiOptimisationStatus( model3 ) = 2 do
  #! >       sol := GurobiSolution( model3 );;
  #! >       number_of_solutions := number_of_solutions + 1;
  