Example: suppose you wanted to classify a large diverse number of letters.
One
variable is to alphabetize by last name. But another variable is to use the
date
as the key to classification.

Uhh...if I have several friends who wrote me letters over several years, I
would classify each one's letters by both name and date: the Landis file,
arranged by date, the Severns file, arranged by date...you get the picture.

Jie-san Laushi

Huodau lau, xuedau lau, hai you sanfen xue bulai
_____________________________________________
to email: eliminate redundancy