sub Day_of_Week {
    my ( $year, $month, $day ) = @_;
    
    if ( $month < 3 ) {
        $month += 12;
        --$year;
    }

    my $day_of_week = $day + 2 * $month + int( .6 * ( $month + 1) ) + $year + int( $year / 4 ) - int( $year / 100 ) + int( $year / 400) + 2;
    $day_of_week = int(( $day_of_week / 7 - int( $day_of_week / 7 )) * 7 + .5);

    return $day_of_week;
}

#   From Ovid's post at node 139108 (with some modifications)
#
sub Days_in_Month {
    my ( $year, $month ) = @_;

    my @days_in_month = 
        qw/ 31 28 31 30 31 30
            31 31 30 31 30 31 /;

    if ( --$month == 1 ) {
        return 29 if leap_year( $year );
    }
    return $days_in_month[ $month ];
}

sub leap_year {
    my $year = shift;
    return ( 0 == $year % 4 and 0 != $year % 100 or 0 == $year % 400 ) ? 1 : 0;
}