index on aggregate function

I somewhere read that it is possible to create an index on aggregate functions
in PostgreSQL. Which syntax do I have to use for it?

test=> CREATE TABLE test ( name VARCHAR(32) );
CREATE
test=> CREATE INDEX test_idx ON test lower(name);
ERROR:  parser: parse error at or near "lower"

gives me a parser error.

--

          Regards,

                            Sascha Schumann |
                                 Consultant | finger sas@schell.de
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