Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 [5] => 6 )

a:1
Array ( [0] => 2 [1] => 3 [2] => 4 [3] => 5 [4] => 6 )

b: 6
Array ( [0] => first [1] => 2 [2] => 3 [3] => 4 [4] => 5 [5] => 6 )

---

a: 6
Array ( [0] => first [1] => 2 [2] => 3 [3] => 4 [4] => 5 )

b: 6
Array ( [0] => first [1] => 2 [2] => 3 [3] => 4 [4] => 5 [5] => last )