A program is a set of instructions  that  can  be  compiled  and
  executed by itself.

  Syntax:

     [[attribute-list]]
     PROGRAM comp-unit-identifier [[({file-identifier},...)]];
       [[declaration-section]]
       BEGIN
       {statement};...
       END.

  The 'attribute-list' is one or  more  identifiers  that  provide
  additional information about the compilation unit.

  The 'comp-unit-identifier' specifies the name  of  the  program.
  The  identifier  appears  only  in  the heading and has no other
  purpose within the compilation unit.

  The 'file-identifier' specifies the names of any file  variables
  associated with the external files used by the compilation unit.

  The 'declaration-section' is a VSI Pascal declaration section.

  The 'statement' is any VSI Pascal statement.

  The program  heading  includes  all  information  preceding  the
  program  block.   If  your  program contains any input or output
  routines, you must list all the external file variables that you
  are  using  in  the  compilation unit's heading.  File variables
  listed in a heading must also be declared locally in the  block,
  except for the predeclared file variables INPUT and OUTPUT.

  The INPUT identifier corresponds to a predefined  external  file
  that  accepts  input  from  the  default  device  (usually, your
  terminal); the OUTPUT identifier  corresponds  to  a  predefined
  external  file that sends output to the default device (usually,
  your terminal).

  If you redeclare INPUT or OUTPUT in a  nested  block,  you  lose
  access to the default input or output devices.