i = isLattice P
The poset $P$ is a lattice if every pair of vertices has a unique least upper bound and a unique greatest lower bound, i.e., every pair of vertices has a unique meet and a unique join. Equivalently, the poset $P$ is a lattice if it is both a lower semilattice and an upper semilattice.
Clearly, the $n$ chain and the $n$ booleanLattice are lattices.




The middle ranks of the $n$ booleanLattice are not lattices.

The object isLattice is a method function.