i = isRanked P
The poset $P$ is ranked if there exists an integer function $r$ on the vertex set of $P$ such that for each $a$ and $b$ in the poset if $b$ covers $a$ then $r(b)  r(a) = 1$.
The $n$ chain and the $n$ booleanLattice are ranked.







However, the pentagon lattice is not ranked.


This method uses the method rankPoset, which was ported from John Stembridge's Maple package available at http://www.math.lsa.umich.edu/~jrs/maple.html#posets.
The object isRanked is a method function.