Bava Batra

who stated  that it contained an area of twenty griva,  but it contained only fifteen. He  came before Abaye who said unto him, '[Surely] you realized [its size] and accepted.' But did we not learn: THE SALE IS VALID [IF THE DIFFERENCE IS] LESS THAN A SIXTH; [IF IT AMOUNTS] TO A SIXTH, DEDUCTION  MUST BE MADE? — This applies only where [the buyer] is not acquainted with the field, but where he is acquainted with it [it is assumed that] he understood [the conditions] and accepted. 'But,' [argued R. Papa.] 'he said to me, twenty!'  — He replied: '[The seller might say that he meant] that the field was as good  as [one of] twenty. It was taught: R. Jose said: When brothers divide [an estate]  all of them acquire  possession [of their respective shares] as soon as the lot for one of them is drawn.  On what ground [is possession acquired]? — R. Eleazar said: [Possession is acquired in the same way] as [at] the beginning of [the settlement of] the land of Israel. As [at that] beginning, [the acquisition was] by lot, so here [also it is] by lot. Since there, however, [the division was made] through the ballot box  and the Urim and Tummim,  [should not the division] here also [be made] through  the ballot box and the Urim and Tummim? — R. Ashi replied: [The lot alone suffices here] because [in return for] the benefit of mutual agreement  they determine to allow each other to acquire possession [by the lot  alone]. It has been stated: [In the case when] two brothers divided [an estate between them] and a [third] brother arrived from a country beyond the sea, Rab said the division is cancelled,  and Samuel said they relinquish  [thirds from their respective shares for the third brother]. Raba said to R. Nahman: According to Rab, who said that the division is cancelled, it is clear that [we act on the principle that even a definite] decision may be revised; but if so, the division should be cancelled  also in the case where [a partnership] of three was in existence and two of these divided  the property!  — What a comparison! There,  they went [into the matter], from the very beginning, with the intention of [dividing the property between] three;  but here,  they did not enter '[into the matter], at first, with the intention of [dividing the estate between] three. R. Papa said to Abaye: According to Samuel, who said that they relinquish [thirds from their respective shares for the third brother], it appears that [where] a decision [has been arrived at, it] must be adhered to; but, surely, both Rab and Samuel have said:  [If the seller said.] 'I sell you a kor for thirty', he may withdraw even at the last se'ah;  [if, however, he said,] 'I sell you a kor for thirty. [each] se'ah for a sela' [the buyer] acquires  possession of every se'ah as it is measured out for him.  [This shows that even a decision arrived at,  may be upset!]