$a[0] = 1 $b[0] = a
$a[0] = 1 $b[1] = b
$a[1] = 2 $b[2] = c
$a[1] = 2 $b[0] = a
$a[2] = 3 $b[1] = b
$a[2] = 3 $b[2] = c
$a[0] = 1 $b[0] = a
$a[0] = 1 $b[1] = b
$a[1] = 2 $b[2] = c