howto revoke a key that has no secret key

[Doug Barton]

Please don't reply to a message on the list and change the subject line. 
Doing so causes your new topic to show "under" the previous one for 
those using mail readers that thread properly, and may cause your 
message to be missed altogether if someone has blocked that thread.

Instead, save the list address and start a completely new message.

hope this helps,

Doug