OFFSET
2,1
REFERENCES
Anders Björner and Francesco Brenti, Combinatorics of Coxeter groups. Graduate Texts in Mathematics, 231. Springer, New York, 2005.
PROG
(SageMath)
def WeakOrder(W):
L = [CoxeterGroup(W).one()]
G = {}
while len(L)>0:
L2 = set()
for w in L:
G[w] = w.upper_covers()
L2 = L2.union(G[w])
L = L2
return DiGraph(G)
print([Poset(WeakOrder(['B', n])).intervals_number() for n in range(2, 6)])
CROSSREFS
KEYWORD
nonn,more,new
AUTHOR
Ludovic Schwob, May 08 2026
STATUS
approved
