Bava Batra 126 - October 29, 27 Tishrei

Rav Asi ruled that a firstborn who protests, his protest is valid. There is a debate among the Rashbam and Rabbeinu Chananel, about what he is protesting. According to the Rashbam, he is protesting the brothers investing in the item before dividing the property, as he will not receive a double portion on the enhancements. Rabbeinu Chananel explains he is agreeing to receive an equal portion of this property/item but is not giving up on his rights to receive the double portion on other property/items. Rabba limits this statement to grapes that were picked but not if they were turned into wine. Why? If a firstborn gives up his rights to a double portion when dividing a particular property, Rav Pappa and Rav Pappi debate (based on a situation where Rava gave a psak about in a different case) whether Rava held that he gave up rights to the double portion of all the properties or only of that particular property? This debate is based on whether one holds that the firstborn receives rights to his double portion immediately upon the death of the father, even before the land is divided, or whether he receives rights to it only once the property is divided. The Mishna differentiates between a father who says he will not bequeath the double portion to his firstborn and a father who says he will equally divide his portion. The first is not allowed as it goes against the Torah and the second is allowed because it is viewed as a gift. One can use the language of a gift to divide property differently than stated by the Torah. What type of proof can be used to prove one is the firstborn to enable him to receive the double portion?