Oulipo was a silly 'organisation' invented by some writers in Paris after the second world war. The members included mathematics lecturers and writers interested in producing texts according to routines or with constraints. George Perec walked the streets of Paris systematically for some months according to a routine derived from a double latin square, and then wrote about what was happening at each location at a specified time.

I was alluding to the idea easily remembered rules for selecting characters from a text known to the person.