square
a:Array
(
    [0] => x2
    [1] => buggy
    [2] => unfold
    [3] => __construct
)
b:Array
(
    [0] => x2
    [1] => buggy
    [2] => unfold
    [3] => __construct
)
Array
(
    [0] => buggy
    [1] => __construct
)
Array
(
    [0] => buggy
    [1] => __construct
)