Actually, the only natural backtracking mechanism found in Perl is in regular expressions. Backtracking is what I use to determine primeness of numbers using regular expressions, it's what's used in the Cookbook when regular expressions are used to solve Diophantine equations, and its used in my reduction of 3-CNF-SAT to regular expressions http://perl.plover.com/NPC/NPC-3SAT.html.

Abigail