0 => ab
1 => a
k => ab
k => a
k => ab
array(1) {
  [0]=>
  int(5)
}
k2 => ab
k1 => 6
2 => 7
3 => k2
k1 => 9
10 => ab
k2 => ab
k1 => 12
array(1) {
  [0]=>
  int(13)
}
11 => k2
k1 => 14
array(1) {
  [15]=>
  string(2) "ab"
}