anchor.diff:  
   %% @doc Return the date one day later.
   next_day({{Y,M,D},T} = Date) ->
  -	case last_day_of_month(Y,M) of
  +	case calendar:last_day_of_the_month(Y,M) of
   		D -> 
   			{{Y1,M1,_},T1} = next_month(Date),
   			{{Y1,M1,1},T1};
  
positive.code: 	diff({YMD1,{H1+24,I1,S1}},NextDate2);
  diff({{Y1,M1,D1},T1}, {{Y2,M2,D2},_} = Date2) when D2 > D1 ->
  	NextDate2 = next_month(Date2),
  	diff({{Y1,M1,D1+last_day_of_month(Y2,M2)},T1},NextDate2);
  diff({{Y1,M1,D1},T1}, {{_,M2,_},_} = Date2) when M2 > M1 ->
  	NextDate2 = next_year(Date2),
  	diff({{Y1,M1+12,D1},T1},NextDate2);
  
negative.code:     timesince/2,
  	timesince/3,
  	
  	days_in_year/1,
  	
  	prev_year/1,
  