intersect of array-containing arrays

#objective
to propagate how great built-in functions are

baseline

$arr1 = ["a", "b"];
$arr2 = ["a", "c"];
var_export(array_intersect($arr1, $arr2));
//array (
//  0 => 'a',
//)

Note: Two elements are considered equal if and only if (string) $elem1 === (string) $elem2. In words: when the string representation is the same.
-- array_intersect/note

so what if the parameters were arrays of array(and so on)?

$arr3 = [["a"], ["b"]];
$arr4 = [["a"], ["c"]];
var_export(array_intersect($arr1, $arr2));
// this causes "PHP Notice:  Array to string conversion"
// and echoes
// array (
//   0 => 
//   array (
//     0 => 'a',
//   ),
//   1 => 
//   array (
//     0 => 'b',
//   ),
// )
// because (string)["a"] or (string)["b"] or (string)["c"] should be "Array"

solution

use array_uintersect;

var_export(array_uintersect($arr3, $arr4, function($a, $b) { if ($a == $b) return 0; else return -1;}));
//array (
//  0 => 'a',
//)

and read document.