+ return ( days )
+}
+
+# isSameSeason
+#
+# Check if two months fall in the same "season" (defined by estimated pollution rate).
+#
+# @param month Month index to test
+# @param month_ref Month to compare to
+#
+.isSameSeason = function(month, month_ref)
+{
+ if (month_ref %in% c(11,12,1,2)) #~= mid-polluted
+ return (month %in% c(11,12,1,2))
+ if (month_ref %in% c(3,4,9,10)) #~= high-polluted
+ return (month %in% c(3,4,9,10))
+ return (month %in% c(5,6,7,8)) #~= non polluted
+}
+
+# isSameDay
+#
+# Monday=Tuesday=Wednesday=Thursday ; Friday, Saturday, Sunday: specials.
+#
+# @param day Day index to test
+# @param day_ref Day index to compare to
+#
+.isSameDay = function(day, day_ref)
+{
+ if (day_ref %in% 1:4)
+ return (day %in% 1:4)
+ return (day == day_ref)
+}