static function sequence ($list)
  {
    $a = new AppendIterator;
    foreach (iterator ($list) as $it)
      $a->append (iterator ($it));
    return new static ($a);
  }
static function sequence ($list)
  {
    $a = new AppendIterator;
    foreach (iterator ($list) as $it)
      $a->append (iterator ($it));
    return new static ($a);
  }
static function sequence ( $ list ) { $ a = new AppendIterator ; foreach ( iterator ( $ list ) as $ it ) $ a -> append ( iterator ( $ it ) ) ; return new static ( $ a ) ; }
Concatenates the specified iterables and iterates them in sequence.

>**Caution**
<p><br>When using {@see iterator_to_array()} to copy the values of the resulting sequence into an array, you
have to set the optional `use_key` argument to `FALSE`.<br>
When `use_key` is not `FALSE` any keys reoccuring in inner iterators will get overwritten in the returned array.
<p><br>When using {@see Flow::all()} the same problem may occur.<br>
You can use {@see Flow::pack()} or {@see Flow::reindex()} instead, if you need a monotonically increasing
sequence of keys.

@param mixed $list A sequence of iterables.
@return static
Concatenates the specified iterables and iterates them in sequence .