Menachos 3:6-7

Menachos 3:6

The following things preclude one another (i.e., you can’t have one without the other): the two male goats of Yom Kippur, the two lambs of Shavuos, the two loaves of Shavuos, the two rows of showbread, the two dishes of frankincense with the showbread – the rows of showbread and the dishes of frankincense also preclude one another – the two kinds of bread brought by a nazir, the three components of the red heifer ceremony (cedar, hyssop and scarlet wool), the four kinds of bread of a thanksgiving offering, the four species of the lulav, and the four components of a metzora’s purification (cedar, hyssop, scarlet wool and two live birds). The seven sprinklings of the red heifer preclude one another (i.e., if one is missing, the ceremony is invalid) and the seven sprinklings between the staves of the Aron, towards the curtain and on the golden altar all preclude one another.

Menachos 3:7

The seven branches of the menorah preclude one another, as do the seven lamps (i.e., if one is missing, it cannot be used). The two portions to be written in a mezuzah preclude one another – even the absence of a single letter precludes them! The four portions to be written in tefillin preclude one another, as does even a single letter. The four tzitzis preclude one another because all four of them combined constitute a single mitzvah; Rabbi Yishmael says that they are four separate mitzvos.