`.list'
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   Control (in conjunction with the `.nolist' directive) whether or not
assembly listings are generated.  These two directives maintain an
internal counter (which is zero initially).   `.list' increments the
counter, and `.nolist' decrements it.  Assembly listings are generated
whenever the counter is greater than zero.

   By default, listings are disabled.  When you enable them (with the
`-a' command line option; see Command-Line Options: Invoking.), the
initial value of the listing counter is one.