(Mishnah): A man may not neglect Peru u'Rvu unless he has children. Beis Shamai say, he must have (at least) two sons;

Beis Hillel say, he must have a male and a female - "Zachar u'Nekevah Bera'am."

If a man married a woman and she did not give birth in 10 years, he may not neglect Peru u'Rvu;

If he divorced her, she may marry another man, and the latter man may keep her for 10 years without children;

If she miscarried, we count 10 years from the miscarriage.

A man is commanded "Peru u'Rvu, but a woman is not;

R. Yochanan ben Berokah says, about both of them (Adam and Chavah) it says "va'Yevarech Osam Elokim va'Yomer Lahem Elokim Peru u'Rvu..."

(Gemara): Beis Shamai say, [he fulfills the Mitzvah through] two sons, for it says about Moshe "Gershom" and "Eliezer".

Beis Hillel say, he must have a male and a female. They learn from the creation of the world - "Zachar u'Nekevah Bera'am."

(R. Bun): [Beis Hillel] teach that [even] a male and a female [suffice, and all the more so two males]. If not (rather, they require specifically a male and a female), this should have been taught (in Maseches Eduyos) with the places in which Beis Shamai are lenient and Beis Hillel are stringent!

Note: This assumes that if Beis Hillel require specifically a male and a female, Beis Shamai allow either this, or two males. If Beis Shamai require specifically two males, each of them have their own stringency!

Sons of sons are like sons. Sons of daughters are not like sons. The son of a son and the daughter of a daughter count (like a son and daughter, respectively). The daughter of a son, or the son of a daughter, do not count (neither counts like a son. We explained this like HA'GAON RAV C. KANIEVSKY, SHLITA.)

An Ailonis, Seris and people who are not proper to have children do not count.