anchor.diff:  
   -behaviour(gen_server).
   
  --export([start_link/0, get_entity/2, get_entity/3, get_tag/1, get_branch/1, put_entity/3, put_entity/4, put_tag/2, put_tag/4, put_branch/2, put_branch/4, get_meta/2, get_meta/1, put_meta/3, list_meta/0, list_entities/1, list_entities/2, list_tags/0, list_branches/0, version/0, version_string/0, delete_tag/1, delete_branch/1, delete_entity/3]).
  +-export([start_link/0, get_entity/2, get_entity/3, get_tag/1, get_branch/1, put_entity/3, put_entity/4, put_tag/2, put_tag/4, put_branch/2, put_branch/4, get_meta/2, get_meta/1, put_meta/3, list_meta/0, list_entities/1, list_entities/2, list_tags/0, list_branches/0, version/0, version_string/0, delete_tag/1, delete_branch/1, delete_entity/3, delete_meta/2]).
   
   -export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).
   
  
positive.code:     ok.
  
  delete_helper(Name, Kind, Commit, StoreMod) ->
      ok.
  
  immediately_affected_entities(_Name, node, _Tree, _StoreMod) ->
      % removing a node doesn't affect anything else
  
negative.code: 		error_logger:warning_msg("No groups for tree with hash ~p~n", [wallaroo_db:identity(Tree)]),
  		[]
  	end,
      Groups ++ Features;
  immediately_affected_entities(Name, parameter, Tree, StoreMod) ->
      % removing a parameter affects groups or features that installed that parameter 
      % and subsystems that are interested in that parameter
      lists:flatten([case wallaroo_tree:get_path([xlate_what(Kind)], Tree, StoreMod) of
  		       {value, Entities} ->
  			   [{[xlate_what(Kind), E], ObjPrime} ||
  			       {E, Obj} <- wallaroo_tree:children(Entities, StoreMod),
  			       (ObjPrime = elim_param(Name, Obj)) =/= Obj];
  		       none ->
  			   error_logger:warning_msg("No ~ps for tree with hash ~p~n", [Kind, wallaroo_db:identity(Tree)]),
  			   []
  		   end || Kind <- [group, feature, subsystem]]).
  
  % eliminates the feature named DelF from the feature object Fobj
  -spec elim_feature(binary(), wallaby_feature:feature()) -> wallaby_feature:feature().
  