True.

And if this is the case, it will be both in itself and in another too.

How?

Every part is in the whole, and none is outside the whole.

True.

And all the parts are contained by the whole?

Yes.

And the one is all its parts, and neither more nor less than all?

No.

And the one is the whole?

Of course.

But if all the parts are in the whole, and the one is all of them and the
whole, and they are all contained by the whole, the one will be contained
by the one; and thus the one will be in itself.

That is true.

But then, again, the whole is not in the parts--neither in all the parts,