Two kav [doughs]; the challah of this one was taken by itself, and [the challah] of this one by itself, [and] he then made them into one dough, R' Akiva exempts [the dough], but the Sages obligate [it]. It thus emerges that his stringency is his leniency.

One may take an amount [of dough] for challah from a dough whose challah has not been taken, to make it in taharah, in or-der to continuously separate from it challah of demai, until it spoils. Because challah of demai may be taken from [dough that is] tahor on behalf of [dough that is] tamei and from that which is not in [their] proximity.