We solve directly a general maximin (sustainment, intergenerational-equity) problem. Because the shadow values of a maximin problem do not correspond to the shadow values from a general discounted-utility solution, they correspond to the prices of only a very special competitive economy. Virtual discount factors for the economy arise. They do not correspond to hyperbolic discount factors. Hartwick's rule is derived and generalized naturally to take into account non-autonomous and non-deterministic features of the economy. Under uncertainty, Hartwick's rule is the analytic expression of a form of precautionary principle. Hotelling's rule is a necessary condition, but may be more complex than has been appreciated in simple models. Some interpretations of strong sustainment are special cases of weak sustainment but, paradoxically, may be more difficult to solve. Maximizing welfare or sustaining utility?In this paper, we discuss the conditions for sustaining, primarily 'weakly' sustaining, an abstract economy, on the assumption that it is sustainable. An erudite survey by Pezzey and Toman (2002-3) sums up what they call the neoclassical treatment of weak sustainability. That treatment utilizes a welfare integral, which Pezzey and Toman call general because the force of interest (or instantaneous rate of discount) need not be constant. Let U denote current utility or felicity, a function of a vector of consumption goods C; GPV(t) the general present value (welfare), as of time t; and θ (t) the factor that discounts from time t to time 0. Thensubject to various conditions including transition equations for capital stocks. The problem faced by a planner is a standard control problem, to maximize GPV(t).We thank Urs Brandt, Jon Conrad, Kim Long, the late Philippe Michel, Tapan Mitra, Robert Solow, Koichi Suga, Franz Wirl and three referees for helpful comments and FCAR and SSHRCC for financial support.

A central issue in the study of sustainable development is the interplay of growth and sacrifice in a dynamic economy. This paper investigates the relationship among current consumption, growth, and sustained consumption in two canonical, stylized economies and in a more general context. It is found that the measure of what is sustainable is the maximin value. That value is interpreted as an environmentaleconomic carrying capacity and current consumption or utility as an environmentaleconomic footprint. The time derivative of maximin value is interpreted as total, net investment. It is called durable savings to distinguish it from genuine savings usually computed with discounted utilitarian competitive prices.

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The fundamental problem of economic accounting is to determine a forward‐looking schedule of rentals, user costs or quasi‐rents to provide for the recovery of irreversible investments. The method derived herein relaxes some restrictive assumptions that are common in capital theory. There can be multiple forms of comprehensive capital. Accounting for all forms of capital, including tangible and intangible capital, is symmetrical. The analytical focus becomes one of fixities and frictions and not optimality. Rentals obey inequalities as opposed to marginal conditions. If discounted profit is positive, rentals, depreciation, and capital value are not unique.

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The literature on exploration for non-renewable resources is surveyed. Following a brief synopsis in section 2, section 3 focuses on issues related t o the world market for resources. Section 4 considers more microeconomic supplyrelated issues linked to the exploration of the small region or play. Section 5 turns to the small but growing literature on exploration as a learning process related to R&D. The latter sections pay particular attention to empirical and policy aspects.