ARE-WE-USING : MEXPRARE-WE-USING is a top-level command.
Determines if given lines are being used to justify
any other lines. Notice that the argument is a list of lines,
not a range (i.e. 1 2 3 4 rather than 1--4).
The command format for ARE-WE-USING is:
The arguments have the following meaning:
LINELIST : List of line numbers
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