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─────$DEFINE and $UNDEFINE──────────────────────────────────────────────────
 
     Action
 
     $DEFINE creates a symbolic variable whose existence or value can be
     tested during conditional compilation; $UNDEFINE removes the symbol.
 
     Syntax  $DEFINE symbol-name [= val]
             $UNDEFINE symbol-name
 
     Parameter          Description
 
     symbol-name        A name of up to 31 characters.
 
     val                Any positive or negative INTEGER*4 value.
 
     Remarks
 
     The default is $UNDEFINE, since any symbol name not specified in
     a $DEFINE metacommand tests .FALSE..
 
     The existence of a <symbol-name> is tested by the DEFINED
     conditional expression.
 
     The $DEFINE and $UNDEFINE metacommands can appear anywhere in a
     program, enabling symbol definitions as desired.
 
     Example
 
     $DEFINE  testflag
     $DEFINE  testval = 2
     .
     .
     .
     $UNDEFINE  testflag
 
     The $DEFINE metacommand is equivalent to the /D compiler option.
                                    -♦-