#print
As I said, '.' is set to the last line touched
by any command in the editor.  So if you type
  3p
. will be set to line 3; and then 
  .p
will print the same line.
Try that - 
with the usual trailer, the commands should be

3p
.p
w
q
ready
The file is the same as before.
#create Ref
3p
.p
w
q
#create file
george washington
john adams
thomas jefferson
james madison
james monroe
john quincy adams
#pipe
#copyin
ed file
#user
#uncopyin
#unpipe
tail -4  .copy >X1
#cmp X1 Ref
#log
#next
8.1a 10
8.2a 6
7.2c 2