The minus sign or hyphen (-) in place of a given  name  in  any  path
  name  indicates  a  name  one  generation back.  This substitution is
  valid only for the first given names in the specification.  Once  you
  have specified a given name, you may not use any hyphens further down
  in the chain:  the hyphens must be first in the string.

  For example, if your default directory  is  CDD$TOP.SALES.JONES,  you
  can  specify  the  CORPORATE directory by typing -.-.CORPORATE.  Note
  that -.SALES.-.PRODUCTION is not a legal usage because  the  sequence
  SALES.- is not allowed.