i = isLowerSemilattice P
The poset $P$ is a lower semilattice if every pair of vertices has a unique greatest lower bound (meet).
Clearly, the $n$ chain and the $n$ booleanLattice are lower semilattices.




The middle ranks of the $n$ booleanLattice are not lower semilattices.

However, the lower ranks of the $n$ booleanLattice are nonlattice lower semilattices.



The object isLowerSemilattice is a method function.