Displays the AIP entry's in-use flag. The value is contained in 1
    byte.

                                   NOTE

       In the next two parameters, the integers denoting INDEX
       and LINE are zero based. For example, INDEX 0 refers to the
       first index, and LINE 3 refers to the fourth line.

       The integer n is optional. The present value of the relevant
       pointer is the default.

       References to INDEX and LINE are invalid if the current page
       is a space area management (SPAM) page.