Version #1 - Rashbam - (Rav Huna): (Even though a firstborn does not receive a double portion in (posthumous) improvements that the brothers made to the property), if he insisted 'let us divide, and I will improve my own property' and they improved all the property, he receives a double portion in the improvements.

(Rabah): Presumably, this is if they harvested grapes or olives, but not if they pressed them. (This is a Shinuy (change). They acquire them, like thieves acquire through Shinuy);

(Rav Yosef): Even if they pressed them, the firstborn gets a double portion in the improvements.

Objection: The firstborn is not entitled to a double portion of wine (since the brothers "stole" the grapes and acquired them through Shinuy)!

Version #2 - (R. Chananel cited by Rashbam) - (Rav Huna): If the firstborn said 'I do not forfeit my extra portion', he does not forfeit it (even if they divided the property equally).

(Rabah): Presumably, this is if they harvested grapes or olives, but not if they pressed them (his silence shows that he pardoned his extra share).

(Rav Yosef): Even if they pressed them, the firstborn gets a double portion.

Objection: If they changed from grapes to wine, surely he pardoned his extra share! (End of Version #2)

Answer: Rav Yosef meant that if the wine is worth less than the grapes were worth, the firstborn receives the value of a double portion of the grapes;

This is like Rav Ukva bar Chama said (elsewhere).

Question: Where did he say this?

Answer: Rav Yehudah taught that if a man left grapes or olives to his two sons and they harvested them, the firstborn gets a double portion, even if they pressed them.

Objection: The firstborn is only entitled to a double portion of grapes, but not of wine!

Answer (Rav Ukva bar Chama): (Even) if the wine is worth less than the grapes were worth, the firstborn receives the value of a double portion of the grapes.

(Rav Asi): If a firstborn took a portion like a regular son, he pardoned his extra share.

Question: What did he pardon?

Answer #1 (Rav Papa citing Rava): He pardoned his extra share in that field.

He holds that the firstborn does not own his extra share until they divide. (He cannot pardon what he does not yet own.)

Answer #2 (Rav Papi citing Rava): He pardoned his extra share in all the property.

He holds that a firstborn owns the extra even before they divide. (Since he pardoned his extra share in this field, he pardoned his extra share in all the property.)

Rav Papa and Rav Papi did not explicitly hear Rava say this. Rather, they derived their opinions from the following episode.

A firstborn sold his property and that of his brothers. His brothers went to eat dates of the property. The buyer hit them. Their relatives complained to Rava.

Rava: The sale is void.

Rav Papi understood that the sale is void regarding the brothers' property, but the sale of his own property stands;

Rav Papa understood that the entire sale is void.

(Chachamim of Eretz Yisrael): If a firstborn sold (his extra share) before the property was divided, the sale is void.

They hold that the firstborn does not own his extra share until they divide.

The Halachah is, a firstborn owns his extra share even before they divide.

Mar Zutra of Darishba (a firstborn) divided a basket of peppers equally with his brothers.

(Rav Ashi): Since you pardoned your extra share in the peppers, you pardoned your extra share in all the property.

(Mishnah): If one said 'Ploni my firstborn will not receive a double portion', or 'Almoni my son will not inherit with his brothers', this does not take effect, for he stipulated against the Torah.

If one (a Shechiv Mera, one who fears lest he die from his illness) stipulated how much each son should receive, and gave some sons more than others, or gave the firstborn as much as the others, this takes effect;

If he said that this was their inheritance, it does not take effect;

If he wrote at the beginning, middle or end that it is a gift, it takes effect.

(Gemara) Suggestion: Our Mishnah is not like R. Yehudah, who says that a stipulation against the Torah takes effect.

(Beraisa - R. Meir): If one said 'you are Mekudeshes to me on condition that you have no claim against me for food, clothing or Onah (Bi'ah at the proper frequency)', she is Mekudeshes, and the stipulation is void;

R. Yehudah says, the stipulation takes effect in monetary matters (food and clothing).

Rejection: Our Mishnah is even like R. Yehudah. There, she accepted Kidushin with the stipulation, and she pardoned her rights. Here, the son does not pardon his inheritance.

(Rav Yosef): If (we do not know who is Reuven's firstborn, and) he said 'my son Ploni is my firstborn', Ploni receives a double portion;

If he said 'he is a firstborn', he does not receive a double portion. Perhaps he meant that he is a firstborn to his mother.

Shimon: I am sure that Levi is a firstborn. (There was also a second witness.)

Rabah bar bar Chanah: How do you know?

Shimon: His father called him 'foolish firstborn'.

Rabah bar bar Chanah: A firstborn to the mother is also called a foolish firstborn.

Reuven: I am sure that this man (Shichchas) is a firstborn.

R. Chanina: How do you know?

Reuven: When people with eye-aches would come to his father, the father would tell them 'go to my son Shichchas. He is a firstborn, so his spit will heal you.'

Question: Perhaps he is a firstborn to his mother (but not to his father)!

Answer: If so, his spit would not heal.

(R. Ami): (A Tumtum is one whose genitals are covered, so we cannot tell if he is a male or female.) If (the skin covering the genitals of) a (firstborn) Tumtum was torn and he was found to be a male, he does not receive a double portion. "V'*Hayah ha'Ben* ha'Bechor la'Seni'ah" - he must be (recognizably) a son from his Havayah (birth).