The 
!!
 history substitution gives a copy of the previous command. Most people use it to re-execute the previous command line. Sometimes I want to repeat a cycle of two commands, one after the other. To do that, I just type 
!-2
 (second-previous command) over and over:
%vi plot... %vtroff -w plot... %!-2vi plot ... %!-2vtroff -w plot ...
You can cycle through three commands with 
!-3
, four commands with 
!-4
, and so on. The best part is that if you can count, you never have to remember what to do next. 
:-)
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