anchor.diff:  
   encode_ssn(SSN) ->
   	case SSN of
  -		undef ->
  +		undefined ->
   			{0, <<>>};
   		_ ->
   			{1, <<SSN:8>>}
  
positive.code: 			<<PointCode:16/little, Remain/binary>> = BinPC;
  		_ ->
  			Remain = BinPC,
  			PointCode = undef
  	end,
  	{Remain, PointCode}.
  
  
negative.code: parse_gt(BinGT, GTind) ->
  	case GTind of
  		?SCCP_GTI_NO_GT ->
  			undefined;
  		?SCCP_GTI_NAT_ONLY ->
  			% Figure 7/Q.713
  			<<Odd:1, Nature:7, Digits/binary>> = BinGT,
  