(1) It is true that some suttas describe Samma Samadhi as the four rupavacara jhanas.
– However, that probably means being able to get into all four jhanas at the COMPLETION of Samma Samadhi at the Arahant stage.
– We can easily see that getting into jhanas is NOT NECESSARY to attain at least the Sotapanna and Sakadagami stages. If ANY PERSON attains even the first Ariya OR anariya jhana, that person will be born in a Brahma realm, and WILL NOT be born in human or Deva realms. But we know that a Sotapanna could be reborn in human or Deva realms and a Sakadagami can be reborn in a Deva realm. That proves that even the first jhana is not necessary to attain the Sotapanna or Sakadagami stages.
(2). The problem is with the following statement by Lang:
“The Bodhisatta experienced an ariya jhana as a boy and learned anariya jhanas from the 2 teachers.”
The jhana that the Bodhisatta experienced WAS an anariya jhana. To get to an Ariya jhana, one must have attained a magga phala. The Bodhisatta attained ALL stages of magga phala during the night of his Enlightenment. A Bodhisatta CANNOT get to any stage of magga phala BEFORE the night of Enlightenment.
– The Bodhisatta attained the first anariya jhana as a boy under a rose apple tree per that account.
– Later on, he attained ALL anariya jhanas with the help of those two yogis, Alara Kalama and Uddaka Ramaputta.