Source: He (Rebbi Chiya bar Aba) probably learned this from the words "Ra'ah ba'Mageifah",

How Many Sets of Stones #1: Yerushalmi: 'There were three kinds of stones - the stones that they took to the inn, the stones that Yehoshua ordered them to place underneath the feet of the Kohanim and the stones that Moshe gave them'.

How Many Sets of Stones #2: Rebbi Yitzchak (Rebbi Chaninan) said 'It is clear that there were four kinds of stones'.

Support: Rebbi Si'man bar Z'vida agreed.

Proof: 'Because', he said (bearing in mind that Yehoshua talked of 'Stones of Remembrance') if he was referring to the stones that they set up in the inn - they were only placed there temporarily and hidden; If he was referring to the stones that he set up under the feet of the Kohanim - they were submerged in the water; And if he was referring to the stones that Moshe gave them - those stones entered Eretz Yisrael together with them?

Conclusion: So which stones was he referring to? He must have been referring to the stones that Yehoshua set up on the banks of the Yarden.

Clarification #1: Rebbi Yehudah in the Tosefta says that they wrote it on the Mizbe'ach.

Clarification #2: In the Yerushalmi however, he says that they wrote it on the stones in the inn. And Rebbi Yossi there holds 'On the stones of the Mizbe'ach'.

Question: According to the opinion that holds 'on the stones of the inn', every day the nations would send their notaries to copy the Torah that was written in seventy languages.

Question (cont.): Whereas according to the opinion that holds 'on the stones of the Mizbe'ach', it only remained temporarily, and then the stones were hidden?

Answer: That this miracle too, occurred there that Hash-m placed understanding into the hearts of each nation to come and copy the Torah (in the short space of time that the Mizbe'ach stood), which was written in seventy languages.

Question: According to the opinion that it was written on the stones of the inn, the Pasuk "And you shall cement it with lime" makes sense. But according to the one that says that it was written on the stones of the Mizbe'ach, why was it necessary to cement it with lime?

Answer: They only cemented it between one stone and the other (but not the entire Mizbe'ach).

Question: Why is the reason not because when the Torah was given, Hash-m offered it to every nation and tongue, but they refused?

Answer: The sin here was great - because after they had it already written in their hands, they did not want to learn it!

Question: The question however remains, that the Gemara in the first Perek of Avodah-Zarah (Daf 2b) tells how they still had an excuse in that they could say 'Did You hold the mountain over our heads like You did to Yisrael?' And as long as they had an excuse, how could their fate be sealed?

Question #1: How could they accept Rachav, seeing as she was descended from the Cana'anim who lived in the land ...

Source: As the Sifri says in Parshas Beha'aloscha (in connection with Rachav) - 'If already someone who came from a forbidden nation about whom the Torah writes "Do not lest anybody live!", yet because she brought herself close, so Hash-m brought her close ... !'

Question #2: And the Gemara also says in Megilah (Daf 14b) that she converted and Yehoshua married her. Whereas here it implies unanimously that they could not accept Cana'anim who lived in Eretz Cana'an?

Answer #1: Perhaps it was due to a Divine command.

Refuted Answer: One cannot answer that before they conquest began they were permitted to accept converts ...

Refutation: Seeing as the writing on the stones occurred before the conquest began, yet they only accepted those who lived outside the border of Yisrael, as Rashi explains.

Answer #2: We can answer however, that in the event that they did Teshuvah when they wrote the Torah, then it was permitted to accept even the Cana'anim who lived there, even according to Rebbi Yehudah ...

Answer #2 (cont.): And the Pasuk "in order that they do not teach you to do ... " pertains to the seven nations too.

Support: In fact, this is implied in the Lashon of the Sifri in Parshas Shoftim ve'Shotrim, which , commenting on the Pasuk "In order that they do not teach you to do ... " - states that this teaches us that if they do Teshuvah, they will not be killed, but they will be accepted'

Support (cont.): It only says 'They will not be killed', implying the same people about whom Hash-m said "Do not let anyone live", is not to be killed (The correct text here is not clear [See Hagahos ve'Tziyunim]).

Support (cont.): And it only says "Do not let anyone live" after Yehoshua began the conquest, since he sent proclamations - "Whoever wishes to make peace, let him make peace; to fight, let him fight ... '.

Support (cont.): So we see, that anyone who wanted to come to peace-terms he did not kill.

Support (concl.): And we have to say that this refers to anyone who wanted to make peace before the first battle began, which was the case with Rachav, who accepted the peace-terms before the battles began.

Conclusion: And Rebbi Yehudah and Rebbi Shimon only argue in connection with those Cana'anim who lived outside the borders of Eretz Yisrael, whether or not, one was permitted to accept them after that ...

Conclusion: In that Rebbi Shimon only needed to say 'So you see that if they do Teshuvah one accepts them', with regard to the Cana'anim who lived outside Eretz Yisrael, after the battles began. To teach us that their Din was equivalent to that of all other nations, whom one is always permitted to accept.