anchor.diff:  				true;
   			(#price{type = tariff, units = messages}) ->
   				true;
  +			(#price{type = #pla_ref{}}) ->
  +				true;
   			(_) ->
   				false
   	end,
  
positive.code: 				true;
  			(#price{type = usage, units = seconds}) ->
  				true;
  			(_) ->
  				false
  	end,
  
negative.code: 	F = fun(#price{type = tariff, units = octets}) ->
  				true;
  			(#price{type = usage}) ->
  				true;
  			(#price{type = #pla_ref{}}) ->
  				true;
  			(_) ->
  				false
  