containers: intersections for Set, along with Semigroup newtype

[Viktor Dukhovni]

On Mon, Dec 21, 2020 at 02:06:33PM -0800, David Casperson wrote:

> Lattices aren't necessarily isomorphic to their duals, even with
> bounded lattices. (Take, for instance, lcm and gcd on the
> non-negative integers.  The primes are atoms, there are no
> co-atoms. [1])

But the non-negative integers with gcd and lcm are surely not a bounded
lattice.  If we introduce an upper bound by restricting attention to
numbers that are factors of some number n > 1, then surely co-atoms
reappear in the form of n/p for each prime factor of n.

-- 
    Viktor.