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    $name  = '' unless defined $name;
    $rank  = '' unless defined $rank;
    $c_num = '' unless defined $c_num;

    foreach ($name, $rank, $c_num) { defined or $_ = '' }

    $_ = '' for grep !defined => ($name, $rank, $c_num);

    $name  = '' if weight($name)  == weight($duck);
    $rank  = '' if weight($rank)  == weight($duck);
    $c_num = '' if weight($c_num) == weight($duck);