# File lib/ri_cal/core_extensions/time/calculations.rb, line 88
        def iso_year_and_week_one_start(wkst)
          iso_year = self.year
          date = ::Date.new(self.year, self.month, self.mday)
          if (date >= ::Date.new(iso_year, 12, 29))
            week_one_start =  Calculations.iso_week_one(iso_year + 1, wkst)
            if date < week_one_start
              week_one_start = Calculations.iso_week_one(iso_year, wkst)
            else
              iso_year += 1
            end
          else
            week_one_start = Calculations.iso_week_one(iso_year, wkst)
            if (date < week_one_start)
              iso_year -= 1
              week_one_start = Calculations.iso_week_one(iso_year, wkst)
            end
          end
          [iso_year, week_one_start]
        end