http://www.perlmonks.org?node_id=1019524


in reply to big bug in Date::Calc?

I think the problem is that you are calling Monday_of_Week() twice: 
($y, $m, $d) = Add_Delta_Days( Monday_of_Week( $week, $year ), 6);

# Change line above to:

($y, $m, $d) = Add_Delta_Days( $year, $month, $day, 6);

First week of 2013: 31/12/2012 to 6/1/2013
Second week of 2013: 7/1/2013 to 13/1/2013

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