On the number of realizations of a Hasse diagram by finite sets
Abraham P. Hillman · Proceedings of the American Mathematical Society · 1955
1 See [l, p. 147].Dedekind gave the order for »g4.R. Church has the order for « = 5 in [5] and M. Ward the order for » = 6 in [6].•See Theorem 5.14 in [4], Birkhoff states that this i3 essentially due to Th. Skolem [2].See also [3].