  We propose a notion of a stable partition in a coalitional game that is
parametrized by the concept of a defection function. This function assigns to
each partition of the grand coalition a set of different coalition arrangements
for a group of defecting players. The alternatives are compared using their
social welfare. We characterize the stability of a partition for a number of
most natural defection functions and investigate whether and how so defined
stable partitions can be reached from any initial partition by means of simple
transformations. The approach is illustrated by analyzing an example in which a
set of stores seeks an optimal transportation arrangement.
