多选题：元包

元包

下面关于元包的判断，哪些是成立的？
*@[ABD](4)

A. $$\lbrack \ a, b, c, d \ \rbrack = \lbrack \ a, b, c, d \ \rbrack$$
B. $$\lbrack \ a, b, b, c \ \rbrack = \lbrack \ b, a, b, c \ \rbrack$$
C. $$\lbrack \ a, b, b, c \ \rbrack = \lbrack \ a, b, c \ \rbrack$$
D. $$\lbrack \ a, b, b, c \ \rbrack = \lbrack \ a, b, b, c \ \rbrack$$



A.$$\lbrack \ a, b, c, d \ \rbrack = \lbrack \ a, b, c, d \ \rbrack$$
B.$$\lbrack \ a, b, b, c \ \rbrack = \lbrack \ b, a, b, c \ \rbrack$$
C.$$\lbrack \ a, b, b, c \ \rbrack = \lbrack \ a, b, c \ \rbrack$$
D.$$\lbrack \ a, b, b, c \ \rbrack = \lbrack \ a, b, b, c \ \rbrack$$


答案：A B D