declare
 function f1 return number is
 begin
   return  1 ;
 end;
 function f1(n number) return number is
 begin
   return  2 ;
 end;
 function f1(n date) return date is
 begin
   <<f1>> 
   declare
     function f1(n number) return number is
     begin
      return  5 ;
     end;
   begin
     null;
     return sysdate+f1( 1 );
   end f1;
   return null;
 end f1;
begin
  dbms_output.put_line(f1(d));
end;
SQL> /
 15 . 03 . 05 

PL/SQL procedure successfully completed.

select *
into v 
from dual 
where 'X'=case when dummy='X' then 'X' end;
/

declare
 v_end number;
 v_begin varchar2( 10 );
 cursor c1 is select dummy function from dual function;
 function f1 (function number)
   return number is
 begin
  <<f1>>
  begin
    null;
  end f1;
  select 'end;' as "procedure"
  into v_begin 
  from dual function ;
  execute immediate 'begin null;'||v_begin;
  return v_end;
 end
 ;
 function 
  f1(d varchar2 :='function f1') 
 return number is
 begin
  execute immediate 'select dummy from dual end' into v_begin ;
  return v_end;
 end f1;
begin
 v_end:=f1(sysdate);
end;
/