I had one or two more points to make today in reference to the ideas I rote own yesterday on Rav Shach's question on the Tosephta.
First of all I am really not sure of what is going on in the Rambam and in Rav Shach. The way I understood the Rambam [Laws of Acquisition 20:14] is when there is an exchange of animals and one is found dead that the seller of that animal has to bring the proof. That is different than in ch 20 law 15 in which an animal is found Treif [it had a puncture in its lung] in which case the buyer has to bring a proof.  I thought and I think the reason for the difference is חזקת הגוף. The animal had חזקת כשרות until the last possible moment. In the case the gemara brings in Ketuboth 76B the bride was found with a blemish and the father has to bring a proof it happened after the engagement. So there we do not go by חזקת כשרות and חזקת הגוף. Nor in the exchange of two animals do we go by חזקת הגוף that it was alive until the last possible minute. Perhaps it is possible to suggest a a reason for the Rambam that is based on Tosphot in Nida page 2b that חזקת השתא cancels חזקה מעיקרא unless some other חזקה comes along to strengthen the חזקה מעיקרא? But then why would that not work for the טבח In ה' מיכרה כ:ט''ו

On a side issue The Ketzot says in a case an object was stolen and it is not know if it was before or after the קנין the proof is upon the buyer. Rav Shach simply points out this is in contradiction to both the Rambam and Rav Joseph Karo-but like almost all other Rishonim like the Rosh and the Ran.

The final idea today is the Ari, Isaac Luria. To intend the intentions can be a long and difficult process. Therefore it is  a good idea to get either the small Sidur of the Reshash or the large one.

The small one seems good to me but I have heard that Rav Mordedchai Sharabi said there were some mistakes in it. I myself used the large one [which has the intentions of the Ari in expanded form by the Grandson of the Reshash.] If one is lacking the background for that I think the best idea is to learn  the Eitz Chaim of the Ari and Reb Chaim Vital.  When to do this? I think after having finished Shas twice. {That is what Reb Shmuel Berenbaum told me.} To do this learning however for me at this point seems to be pointless but I still can see its great value for people that are sensitive to that area of value.

[The Ashlag edition of  the writings of the Arizal are the best.] In any case when it comes to Kabalah, the Ashkenazim world is way too filled with the teachings of the Sitra Achra in disguise.