def intersection(l1, l2):
    """Return intersection of two lists as a new list::
    
        >>> intersection([1, 2, 3], [2, 3, 4])
        [2, 3]
        
        >>> intersection([1, 2, 3], [1, 2, 3, 4])
        [1, 2, 3]
        
        >>> intersection([1, 2, 3], [3, 4])
        [3]
        
        >>> intersection([1, 2, 3], [4, 5, 6])
        []
    """
    intersection = []
    for el in l1:
        if l2.count(el) > 0:
            intersection.append(el)
    
    return intersection