access to execute function without access to it content

[Aleksandr Peshcherskikh <aleksandr(dot)peshcherskikh(at)gmail(dot)com>]

Hello support team!
I wanna do next trick. Create user and deny access on tables to him but
allow to execute stored procedures which are referenced to the denied data.
It's very ordinary use case. But I don't know how to do it in postgresql (if
it is possible of course)
I tried the next way.
1. create database test (for owner postgres)
2. create table test (for owner postgres)
3. create function trytest with simple body "perform * from test;" (for
owner postgres)
4. create user test;
5. grant execute trytest to test
6. revoke select on test from test
Now if I try to execute "trytest" from user "test"  it returns me error
"access denied to table test"
What's wrong do I do?
Is there any way to do what i whant?
Regards, Aleksandr.