How to find out about the functions supported in Postgres 8

In another thread (Re: [GENERAL] Return value of 'serial' column on insert)
Bruno Wolff wrote

...
> You can use the currval function to get the id. Normally the sequence
> will have a name like table_column_seq. In 8.0, there is a function
> you can use to get the sequence name, which is a bit more robust than
> hard coding it.

This sounds well useful. How do I find out what the functions available in
Postgres 8 are, and what their usage and calling parameters are?
Thanks
Laurie

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