IFoo = interface(IUnknown)
  function Method1: HResult;
end;

IFoo2 = interface(IFoo)
  function Method2: Hresult;
end;

TBar = class(IFoo2)
  // Declaration of Method1 and Method2
end;


// Later in the code
var
  Foo: IFoo;
begin
  Foo := TBar.Create;
end;