<?php function F($n){for($c=$n?[--$n]:[];~$n&&$n--;$c=[$n,$c]);return$c;}
Standard input is empty
array(0) {
}
array(1) {
[0]=>
int(0)
}
array(2) {
[0]=>
int(0)
[1]=>
array(2) {
[0]=>
int(1)
[1]=>
array(2) {
[0]=>
int(2)
[1]=>
array(2) {
[0]=>
int(3)
[1]=>
array(2) {
[0]=>
int(4)
[1]=>
array(1) {
[0]=>
int(5)
}
}
}
}
}
}