Overrides implied (default) data typing of symbolic names.
  Statement format:

     IMPLICIT typ (a[,a]...)[,typ (a[,a]...)]...

     typ  Is any data type except CHARACTER*(*).  When "typ"
          is equal to CHARACTER*len, "len" specifies the length
          for character data type.  The "len" is an unsigned
          integer constant or an integer constant expression
          enclosed in parentheses.  The largest valid value of len
          on Tru64 UNIX and Linux is 2147483647 (2**31-1); on OpenVMS
          the largest valid value is 65535.  Negative values are
          treated as zero.

     a    Is an alphabetical character.  If you specify a
          range of alphabetic characters (two characters
          joined by a hyphen), the first character must be
          less than the second.

  The IMPLICIT statement assigns the specified data type to all
  symbolic names that have no explicit data type and begins with the
  specified letter or range of letters.  It has no effect on the
  default types of intrinsic procedures.

  Names beginning with a dollar sign ($) are implicitly INTEGER.
  This implicit type cannot be changed in an IMPLICIT statement.