一、填空题 1 设集合A,B，其中A＝{1,2,3}, B= {1,2}, 则A - B＝____________________; (A) - (B)＝ __________________________ . 2. 设有限集合A, |A| = n, 则 |(A×A)| = __________________________. 3. 设集合A = {a, b}, B = {1, 2}, 则从A到B的所有映射是__________________________ ___________