  Let A be a connected hereditary artin algebra. We show that the set of
functorially finite torsion classes of A-modules is a lattice if and only if A
is either representation-finite (thus a Dynkin algebra) or A has only two
simple modules. For the case of A being the path algebra of a quiver, this
result has recently been established by Iyama-Reiten-Thomas-Todorov and our
proof follows closely their considerations.
