Description: Define set of all projective points in a Hilbert lattice (actually in
any set at all, for simplicity). A projective point is the singleton of
a lattice atom. Definition 15.1 of MaedaMaeda p. 61. Note that item
1 in Holland95 p. 222 defines a point as the atom itself, but this
leads to a complicated subspace ordering that may be either membership
or inclusion based on its arguments. (Contributed by NM, 2-Oct-2011)