Subject: HW 7
From: "William J. Rapaport" <rapaport@buffalo.edu>
Date: Wed, 28 Oct 2009 20:05:47 -0400 (EDT)

A student asks:
"Can a number be a subset of, or equal to, a set?
Like, can 3 be a subset of {3} or {{3}}?"

My reply:
Numbers are not sets (they have no members).
So they can't be subsets, either.
They can, of course, be members of sets.

(That's the simple answer that will enable you to do your HW. There is
a more complex and subtle answer, which I will say more about later, to
the effect that sometimes numbers *can* be sets :-)