How to see the original text of the the function that has been wrapped by “DBMS_DDL.WRAP”

As I’m new to Oracle PL-SQL,I’m trying to be familiar with DBMS_DDL package and I used it to hide my source code,below you can see the example I’m working on:

Declare   v_string varchar2(32676); begin      v_string := 'create or replace function get_os_user                   return varchar2 ' || ' is  ' || ' begin ' ||               ' return (sys_context(''userenv'',''os_user''));' || ' end; ';      execute immediate sys.dbms_ddl.wrap(v_string); end; 

The function get_os_user is created in the function section and In the view mode , I see the non readable hex format of the original function.Now my question is how I can see the original format of the function? The way the book from which I read about the package just said this:

The original text can be viewed in DBA/ALL/USER_SOURCE 

Where is DBA/ALL/USER_SOURCE? Are there other ways to see the original format of wrapped functions and procedures?