Forward declaration in packages

PL/SQL allows for a special subprogram declaration called a forward declaration. It consists of the subprogram specification in the package body, terminated by semicolon. Can use procedure/function in the body, before its defined.

Eg:
create or repalce package body pkg
is
procedure a(...);
procedure b(...);
begin
a(...);
end;
procedure a(...)
begin
null;
end;
end pkg;