anchor.diff:      case module_of(Instr) of
           {value, Mod} ->
               modules_of2(Instructions, [Mod|Acc]);
  +	skip ->
  +	    skip;
           false ->
               modules_of2(Instructions, Acc)
       end.
  
positive.code: %% Check that the modules handled in an instruction set for version X
  %% is a subset of the instruction set for version X-1.
  check_module_subset(Instructions) ->
      do_check_module_subset(modules_of(Instructions)).
   
  do_check_module_subset([]) ->
  
negative.code: modules_of([], Acc) ->
      lists:reverse(Acc);
  modules_of([{V,Instructions}|T], Acc) ->
      %% io:format("modules_of -> "
      %% 	      "~n   V:            ~p"
      %% 	      "~n   Instructions: ~p"
      %% 	      "~n", [V, Instructions]),
      case modules_of2(Instructions, []) of
  	Mods when is_list(Mods) -> 
  	    %% io:format("modules_of -> "
  	    %% 	      "~n   Mods: ~p"
  	    %% 	      "~n", [Mods]),
  	    modules_of(T, [{V, Mods}|Acc]);
  	skip ->
  	    %% io:format("modules_of -> skip"
  	    %% 	      "~n", []),
  	    modules_of(T, Acc)
      end.
   
  modules_of2([], Acc) ->
      lists:reverse(Acc);
  