OFFSET
0,3
COMMENTS
An antichain is a set of sets, none of which is a subset of any other. It is covering if there are no isolated vertices.
The spanning edge-connectivity of a set-system is the minimum number of edges that must be removed (without removing incident vertices) to obtain a set-system that is disconnected or covers fewer vertices.
EXAMPLE
The a(1) = 1 through a(3) = 14 antichains:
{} {} {}
{{1}} {{1}}
{{2}} {{2}}
{{1},{2}} {{3}}
{{1,2}}
{{1,3}}
{{2,3}}
{{1},{2}}
{{1},{3}}
{{2},{3}}
{{1},{2,3}}
{{2},{1,3}}
{{3},{1,2}}
{{1},{2},{3}}
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Gus Wiseman, Sep 10 2019
STATUS
approved