I recently had cause to contact, by mail, several old friends whose addresses I no longer had handy in my head or my little address book. Accustomed to a lifetime of being able to simply look in the phone book for that information, I was dismayed when I found that a good many of them were no longer listed. Now, if they were no longer listed, that meant that they had either moved without my knowledge, changed their phone numbers to unpublished ones, or gone completely cellular. I found it difficult indeed to track down their mailing addresses. Some, I never did manage to find.