But he shall acknowledge the firstborn, the son of the hated, by giving him a double portion of all that is found with him; for he is the first of his strength, the right of the firstborn is his.
English: “For he is the first” — if a man had children while he was a non-Jew and then converted, Rabbi Yochanan said he has no firstborn for inheritance. Why? Because he already had the first of his strength.
On the daf / in context: Children born before conversion count as “the first of his strength.” Therefore a son born after conversion is not the firstborn for inheritance purposes. (A Jewish man who has a child from a non-Jewess or maidservant is different, because those children are not legally “his.”)
Type of Learning
Derash on “reishis ono” applied to a convert.
What Is Learned
A convert who already had children before conversion has no firstborn for inheritance among the children born after conversion.