  In a general fair division model with transferable utilities we discuss
endogenous lower and upper guarantees on individual shares of benefits or
costs. Like the more familiar exogenous bounds on individual shares described
by an outside option or a stand alone utility, these guarantees depend on my
type but not on others' types, only on their number and the range of types.
Keeping the range from worst share to best share as narrow as permitted by the
physical constraints of the model still leaves a large menu of tight guarantee
functions. We describe in detail these design options in several iconic
problems where each tight pair of guarantees has a clear normative meaning: the
allocation of indivisible goods or costly chores, cost sharing of a public
facility and the exploitation of a commons with substitute or complementary
inputs. The corresponding benefit or cost functions are all sub- or
super-modular, and for this class we characterise the set of minimal upper and
maximal lower guarantees in all two agent problems.
