anchor.diff:                  end,
                   ExistingConstraints0, [{SrcPkg, SrcVsn} | NewConstraints]).
   
  +-spec is_version_missing(vsn(),constraint()) -> boolean().
  +is_version_missing({missing}, _Pkg)->
  +    true;
  +is_version_missing(_Vsn, _Pkg)->
  +    false.
   -spec is_version_within_constraint(vsn(),constraint()) -> boolean().
   is_version_within_constraint({missing}, _Pkg)->
  -    nope;
  +    false;
   is_version_within_constraint(_Vsn, Pkg) when is_atom(Pkg) orelse is_binary(Pkg) ->
       true;
   is_version_within_constraint(Vsn, {_Pkg, NVsn}) ->
  
positive.code: -spec valid_version(pkg_name(),vsn(),constraints()) -> boolean().
  valid_version(PkgName, Vsn, PkgConstraints) ->
    Constraints = get_constraints(PkgConstraints, PkgName),
    case lists:any(fun ({L, _}) ->
  		  is_version_within_constraint(Vsn, L) == nope
  	  end,
  	  Constraints) of
  	true ->
  	  io:format("Missing"),
  	  missing;
  	false ->
  	  lists:all(fun ({L, _ConstraintSrc}) ->
  			is_version_within_constraint(Vsn, L)
  		end,
  		Constraints)
  	end.
  
  %% @doc
  
negative.code: 				  {missing, Pkg};
  				Res ->
  				  lists_some(F, Res, PathInd)
  			  end.
  
  
  %% @doc This gathers the dependency constraints for a given package vsn from the
  