The KEY attribute can be applied to record  fields  to  indicate
  that  the  field is to be used as a key field when the record is
  part of an indexed file.

  Syntax:

     KEY [[( n [[, {options},... ]] )]]
     KEY [[( {options},... )]]

  The 'n' represents the key number.  A key number of 0  indicates
  that  the field is the primary key of the record.  All other key
  numbers indicate alternate keys.   The  key  number  must  be  a
  constant  expression  that denotes an integer value in the range
  from 0 through 254.

  See the "HP Pascal Language Reference Manual" for  the  complete
  description of using the KEY attribute.