# Each list has the form [P1,P2,P3,...].
# Each poset P has the form {[i,j],[k,l],...},
#  where [i,j], [k,l], ... are the covering pairs in P.
#
posets1:=[{}]:
posets2:=[{},{[1,2]}]:
posets3:=[{},{[1,2]},{[1,3],[2,3]},{[1,2],[1,3]},{[1,2],[2,3]}]:
posets4:=[{},{[1,2]},{[1,3],[2,3]},{[1,2],[1,3]},{[1,2],[2,3]},{[2
,4],[3,4],[1,4]},{[1,2],[3,4]},{[1,2],[3,4],[1,4]},{[1,2],[2
,4],[3,4]},{[1,3],[2,3],[3,4]},{[1,3],[2,3],[2,4],[1,4]},{[1
,2],[1,3],[1,4]},{[1,2],[1,3],[2,4]},{[1,2],[1,3],[2,4],[3,4
]},{[1,2],[2,3],[2,4]},{[1,2],[2,3],[3,4]}]: