-the year is, according to international standards, the one containing Jan 4.
-The week number is in $1\ldots53$ range ($52$ for non leap years).
+the year is, according to international standards, the one containing Jan 4 or,
+equivalently, the first week which has Thursday in this year. Both of these
+definitions are the same as saying that the first week of the year must contain
+more than half of its days in this year. Accordingly, the week number will
+always be in $1\ldots53$ range ($52$ for non leap years).