Index on tinterval ?

Hello,

  when I want make index on tinterval type, I get this message:

david=> create table t(i tinterval);
CREATE
david=> create index t_i_index on t(i);
ERROR:  Can't find a default operator class for type 704.

I hope, that I can make index - operators such '<','>','=' etc. are
defined.
Does anybody knows, what I need to do ?


                                                thanks,

                                                        David

--
* David Sauer, student of Czech Technical University
* electronic mail: davids@penguin.cz (mime compatible)