  Fairly dividing a set of indivisible resources to a set of agents is of
utmost importance in some applications. However, after an allocation has been
implemented the preferences of agents might change and envy might arise. We
study the following problem to cope with such situations: Given an allocation
of indivisible resources to agents with additive utility-based preferences, is
it possible to socially donate some of the resources (which means removing
these resources from the allocation instance) such that the resulting modified
allocation is envy-free (up to one good). We require that the number of deleted
resources and/or the caused utilitarian welfare loss of the allocation are
bounded. We conduct a thorough study of the (parameterized) computational
complexity of this problem considering various natural and problem-specific
parameters (e.g., the number of agents, the number of deleted resources, or the
maximum number of resources assigned to an agent in the initial allocation) and
different preference models, including unary and 0/1-valuations. In our
studies, we obtain a rich set of (parameterized) tractability and
intractability results and discover several surprising contrasts, for instance,
between the two closely related fairness concepts envy-freeness and
envy-freeness up to one good and between the influence of the parameters
maximum number and welfare of the deleted resources.
