The Boolean lattice
is the partially ordered set consisting of
all subsets of an
-set, ordered by inclusion.
Equivalently, it is the power set of an
-set regarded as a lattice
with meet and join given by intersection and union, respectively.
The elements of rank in
are the
-element subsets, so the
th rank has
elements. The Hasse diagram
of
is the
-hypercube graph.
Meyer (2026) proved that is not a sphere order.