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     This function performs the following actions:
 
        ■ Flushes the file buffers and closes any open handles for
          files or devices owned by the process.
 
        ■ Restores the termination handler vector (Int 22h) from
          PSP:000Ah.
 
        ■ Restores the CTRL+C handler vector (Int 23h) from PSP:000Eh.
 
        ■ Restores the critical-error handler vector (Int 24h) from
          PSP:0012h.
 
     Transfers control to the termination handler.
 
     If the program is returning to COMMAND.COM, control transfers to
     the resident portion, and the transient portion is reloaded if
     necessary. If a batch file is in progress, the next line of the
     file is fetched and interpreted; otherwise, a prompt is issued for
     the next user command.
 
     This function call is typically used to allow user-written
     utilities, drivers, or interrupt handlers to be loaded as ordinary
     .COM or .EXE programs and then remain resident. Subsequent
     entrance to the code is via a hardware or software interrupt.
 
     This function attempts to set the initial memory allocation block
     to the length in paragraphs specified in register DX. If other
     memory blocks have been requested by the application using Int 21h
     Function 48h, they will not be released by this function.
 
     Other methods of performing a final exit are Int 20h, Int 21h
     Function 00h, Int 21h Function 4Ch, and Int 27h.
 
     The return code may be retrieved by a parent process through Int
     21h Function 4Dh (Get Return Code). It can also be tested in a
     batch file with an IF ERRORLEVEL statement. By convention, a
     return code of zero indicates successful execution, and a nonzero
     return code indicates an error.
 
     This function should not be called by .EXE programs that are
     loaded at the high end of the transient program area (linked with
     the /HIGH switch), because doing so reserves the memory that is
     normally used by the transient part of COMMAND.COM. If COMMAND.COM
     cannot be reloaded, the system will fail.
 
     This function should be used instead of Int 27h because it
     supports return codes, allows larger amounts of memory to be
     reserved, and does not require CS to contain the segment of the
     program segment prefix.
 
     [Version 3.0+]
     If the program is running on a network, it should remove all locks
     it has placed on file regions before terminating.
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