Being as the Indefinite Other

I hit on a tentative, succinct definition of being yesterday, as "the indefinite other." Using the example, "Motion is," which had been discussed in the Sophist seminar only a few minutes earlier, I suggested that the assertion amounts to saying that motion is other than all of the other things, but that in saying that motion is, we don't specify the other things or the relations between motion and the other things. Someone pointed out, however, that it's possible to say that something is other without saying that it (really) is. Thus, "Unicorns are other than elephants" is consistent with "Unicorns are not." However, in the seminar on the Sophist, we've already agreed there's an extended sense of being that includes the being of nonbeing; that is, "Nonbeing is," and "Nonbeing is other than being."