Re: set of a set etc.

On Tue, 19 Jul 2005, G. Frege wrote:

> "The distinction between x and {x} is one of the merits of Peano's
> symbolic logic, as well as Frege's. On the basis of our theory of
> classes, the necessity for the distinction is of course obvious. But
> apart from this, the following consideration makes the necessity
> apparent. Let /a/ be a class; then the class whose only member is /a/
> has only one member, namely /a/, while /a/ may have many members. Hence
> the class whose only member is /a/ cannot be identical with /a/.*"
>
The difference between a, {a}, {{a}} and {{{a}}} is a is something
{a} is a in a box, {{a}} is a in a box within a box and {{{a}}}
is a in a box within a box within yet another box and etc for
so on.
.