anchor.diff:      case dderef(G0, Bs) of
   	{_} -> instantiation_error(St);		%Must have something to call
   	G1 ->
  -	    case catch {ok,well_form_goal(G1, Next, Cut, Label)} of
  -		{erlog_error,E} -> erlog_error(E, St);
  -		{ok,GC} -> GC			%Body and cut
  +	    try
  +		well_form_goal(G1, Next, Cut, Label)
  +	    catch
  +		throw:{erlog_error,E} ->
  +		    erlog_error(E, St)	        %Add state to error
   	    end
       end.
   
  
positive.code: 
  %% Error types.
  -export([erlog_error/1,erlog_error/2,type_error/2,type_error/3,
  	 instantiation_error/0,instantiation_error/1,permission_error/4]).
  
  %%-compile(export_all).
  
  
negative.code:     case Dm:asserta_clause(Dr0, Functor, Head, Body) of
  	{ok,Dr1} -> Db#db{ref=Dr1};
  	error ->
  	    permission_error(modify, static_procedure, pred_ind(Functor))
      end.
  
  assertz_clause({':-',H,B}, Db) -> assertz_clause(H, B, Db);
  