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function ISOWeekNumber(AYear, AMonth, ADay: Word; CMode: integer): integer;
const
  dOffset  : array[1..7] of Byte = (6, 7, 8, 9, 10, 4, 5);
var
  Present, StartOfYear  : TDateTime;
   FirstDayOfYear, WeekNumber, NumberOfDays, RYearOfWeekNumber: integer;
begin
  Present      := EncodeDate(AYear, AMonth, ADay);
   StartOfYear    := ENcodeDate(AYear, 1, 1);
   FirstDayOfYear  := dOffset[DayOfWeek(StartOfYear)];
   NumberOfDays  := Trunc(Present - StartOfYear) + FirstDayOfYear;
   WeekNumber    := NumberOfDays div 7;
   if  WeekNumber = 0 then
     Result := ISOWeekNumber(AYear - 1, 12, 31, CMode)
   else begin
     RYearOfWeekNumber  := AYear;
       if  WeekNUmber = 53 then begin
         if  DayOfWeek( EncodeDate(AYear, 12, 31) ) < 5 then begin
             RYearOfWeekNumber := AYear + 1;
               WeekNumber := 1;
           end;
       end;
       if  CMode = 1 then
         Result := WeekNumber
       else
         Result := RYearOfWeekNumber;
   end;
end;                    

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function ISOWeekDate(AWeek, AYear: integer): TDateTime;
const
  dOffset  : array[1..7] of Byte = (6, 7, 8, 9, 10, 4, 5);
var
  StartOfYear  : TDateTime;
   FirstDayOfYear  : integer;
begin
  StartOfYear    := EncodeDate(AYear, 1, 1);
   FirstDayOfYear  := dOffset[DayOfWeek(StartOfYear)];
   Result      := StartOfYear + (AWeek * 7) - FirstDayOfYear;
end;