Assumption: Now we are thinking that Menatzpach (the variant forms of these five letters) are closed (i.e. later Nevi'im were Mechadesh the forms of the final letters).

Question: Shabbos (104a) connotes oppositely!

Citation (104a) - Question: Granted, if one made an open letter closed, he improved it, like Rav Chisda taught (that the [final] Mem and Samuch stood miraculously);

Citation (cont.): However, if one made a closed letter open, he worsened it, for R. Yirmeyah taught that Nevi'im taught Menatzpach! (Since there was a final Mem at Matan Torah, we must say that the regular Mem came later.)

Inference: Menatzpach are open (the forms of the non-final letters)!

Answer (Ri): The Gemara in Shabbos concludes and teaches [that Menatzpach are open]. It knew Rav Chisda's teaching from the beginning. Also, it was discussing the open letters beforehand. It needed to establish Menatzpach to be open, so Rav Chisda's teaching would not be difficult;

Here, the Gemara means "do you think that this is reasonable?! It says "Eleh ha'Mitzvos" (Nevi'im cannot change anything)! This refutes [R. Yirmeyah] whether Menatzpach are open or closed.

Further, if you will say that they are closed, Rav Chisda's teaching is difficult, that the Mem and Samech [stood miraculously in the Luchos].

Support: Also R. Tam explained like this. He changed the text in Sefer ha'Yashar to read "Menatzpach Tzofim Armum" like "Kol Tzofayich", i.e. Nevi'im.

"Tzofim mi'Har Efrayim" were from 200 Nevi'im, i.e. Tzofim that were established for Yisrael.

These Tzofim were after Amon burned the Torah (and it was not known which forms are the final letters). They are called Tzofim due to the semblance of this word to Menatzpach.

Explanation: The Gemara asks "do you think that this is reasonable?! It says "Eleh ha'Mitzvos"! Also, Rav Chisda taught that the Mem and Samech in the Luchos...

The Gemara answers "indeed, they were [in the Luchos]. This is not difficult. R. Yirmeyah establishes them to be closed. When [the Sugya] arises in Megilah, we ask from Rav Chisda's teaching.

Observation: This is the Gemara's way. If we hold one way, we reject this.

We ask also from "Eleh ha'Mitzvos", and answer properly.

From the Sugya in Megilah and Shabbos, it is clear that R. Yirmeyah meant that Tzofim said Menatzpach, both the open and closed forms, like the Gemara concludes.