A new proof of Whitman's embedding theorem (Q1891749)

In 1946 P. M. Whitman proved that every lattice can be embedded into a partition lattice. Since partition lattices can be embedded into subgroup lattices, it follows that every lattice is isomorphic to a sublattice of the subgroup lattice of a suitable group. The author gives a direct and relatively short proof of this result utilizing a basic construction of combinatorial group theory: the HNN-extension.