Sudoku solver in three lines explained

Sudoku solver in three lines explained: "
In previous posts I produced a four line sudoku solver and then went on to explain it. After having watched a C programmer's approach to it I am down to under three lines. Here it is and how it works.

use integer;@A=split//,<>;sub R{for$i(0..80){next if$A[$i];my%t=map{$_/9
==$i/9||$_%9==$i%9||$_/27==$i/27&&$_%9/3==$i%9/3?$A[$_]:0=>1}0..80;R($A[
$i]=$_)for grep{!$t{$_}}1..9;return$A[$i]=0}die@A}R"