--------------------- 1
<0> [0] set append
<1>  append
<2>  append
<3> [3] set append
--------------------- 2
<0> [0] set append
<1>  append append
<2>  append append
<3> [3] set append
--------------------- 3
<0> [0] set append
<1>  append append append
<2>  append append append
<3> [3] set append
--------------------- 4
<0> [0] set append
<1>  append append append append
<2>  append append append append
<3> [3] set append
--------------------- 5
<0> [0] set append
<1>  append append append append append
<2>  append append append append append
<3> [3] set append