def truth_table(n):
    """
    INPUT: `n` is an integer >= 1. 
    OUTPUT: A list of lists of Booleans. 
    
    Each sub-list represents one row of a truth table with  `n` boolean variables.
    
    There should be a total of `2 ** n` inner lists, each containing `n` items, representing
    the value of each of the `n` variables. There is no column for the output, since there is
    no boolean expression to evaluate. 
    
    >>> test_one = truth_table(1)
    >>> result_one = [[False], [True]]
    >>> type(test_one) is list and len(test_one) == 2 ** 1
    True
    >>> all([item in result_one for item in test_one])
    True
    
    >>> test_two = truth_table(3)
    >>> result_two = [[False, False, False], [True, False, False], [False, True, False], [False, False, True], [True, True, False], [True, False, True], [False, True, True], [True, True, True]]
    >>> type(test_two) is list and len(test_two) == 2 ** 3
    True
    >>> all([item in result_two for item in test_two])
    True
    
    """
    if n == 1:
        return [[False], [True]]
    
    recurse = truth_table(n-1)
    
    res = []
    for row in recurse:
        add_true = row + [True]
        add_false = row + [False]
        res.append(add_true)
        res.append(add_false)
    
    return res