The ghosts of forgotten things: A study on size after forgetting

Forgetting is removing variables from a logical formula while preserving the constraints on the other variables. In spite of being a form of reduction, it does not always decrease the size of the formula and may sometimes increase it. This article discusses the implications of such an increase and analyzes the computational properties of the phenomenon. Given a propositional Horn formula, a set of variables and a maximum allowed size, deciding whether forgetting the variables from the formula can be expressed in that size is $D^p$-hard in $\Sigma^p_2$. The same problem for unrestricted propositional formulae is $D^p_2$-hard in $\Sigma^p_3$. The hardness results employ superredundancy: a superirredundant clause is in all formulae of minimal size equivalent to a given one. This concept may be useful outside forgetting

Denial of Death and Economic Behavior

We model denial of death and its effect on economic behavior. Attempts to reduce death anxiety and the possibility of denial of mortality-relevant information interact with intertemporal choices and may lead to time-inconsistent behavior and other "behavioral" phenomena. In the model, repression of signals of mortality leads to underconsumption for unsophisticated individuals, but forward-sophisticated individuals may over-consume in anticipation of future denial and may seek ways to commit to act according to one's mortality prospects as currently perceived. We show that the mere possibility of engaging in this kind of denial leads to time-inconsistent but efficient behavior. Refusal to face up to the reality of death may help explain a wide range of empirical phenomena, including the underutilization of tax-advanced inter vivos gifts and inadequate purchase of life insurance.

Beyond Hypertree Width: Decomposition Methods Without Decompositions

The general intractability of the constraint satisfaction problem has motivated the study of restrictions on this problem that permit polynomial-time solvability. One major line of work has focused on structural restrictions, which arise from restricting the interaction among constraint scopes. In this paper, we engage in a mathematical investigation of generalized hypertree width, a structural measure that has up to recently eluded study. We obtain a number of computational results, including a simple proof of the tractability of CSP instances having bounded generalized hypertree width

Against the realistic interpretation of the Theory of Relativity

The Theory of Relativity has been portrayed as a theory that redefined the way we look at the cosmos, enabling us to unlock the reality we live in. Its proponents are constantly reminding us of how Einstein managed to reveal the true nature of the universe with his groundbreaking theory, which has been proved multiple times until now. Yet, philosophy of science teaches us that no theory has any privileged connection with what we call reality per se. The role of science is to formulate models of the cosmos we see and not to try to interpret or reveal reality. This paper tries to show how this holds true even for the famous relativity theory, by showing specific objections to the connection of the theory with the Holy Grail of philosophers. By analyzing various subjects related to the theory, from the twins’ paradox to the GPS satellites, this paper illustrates that relativity is much less connected to reality than what we would like to think. At the end, what Einstein’s theory provides is nothing more than a way to formalize the interactions of the world but without being able to make any claims whatsoever regarding the ‘reality’ of its conclusions

Belief Revision with Uncertain Inputs in the Possibilistic Setting

This paper discusses belief revision under uncertain inputs in the framework of possibility theory. Revision can be based on two possible definitions of the conditioning operation, one based on min operator which requires a purely ordinal scale only, and another based on product, for which a richer structure is needed, and which is a particular case of Dempster's rule of conditioning. Besides, revision under uncertain inputs can be understood in two different ways depending on whether the input is viewed, or not, as a constraint to enforce. Moreover, it is shown that M.A. Williams' transmutations, originally defined in the setting of Spohn's functions, can be captured in this framework, as well as Boutilier's natural revision.Comment: Appears in Proceedings of the Twelfth Conference on Uncertainty in Artificial Intelligence (UAI1996

A ten-year follow-up of a study of memory for the attack of September 11, 2001: Flashbulb memories and memories for flashbulb events.

Within a week of the attack of September 11, 2001, a consortium of researchers from across the United States distributed a survey asking about the circumstances in which respondents learned of the attack (their flashbulb memories) and the facts about the attack itself (their event memories). Follow-up surveys were distributed 11, 25, and 119 months after the attack. The study, therefore, examines retention of flashbulb memories and event memories at a substantially longer retention interval than any previous study using a test-retest methodology, allowing for the study of such memories over the long term. There was rapid forgetting of both flashbulb and event memories within the first year, but the forgetting curves leveled off after that, not significantly changing even after a 10-year delay. Despite the initial rapid forgetting, confidence remained high throughout the 10-year period. Five putative factors affecting flashbulb memory consistency and event memory accuracy were examined: (a) attention to media, (b) the amount of discussion, (c) residency, (d) personal loss and/or inconvenience, and (e) emotional intensity. After 10 years, none of these factors predicted flashbulb memory consistency; media attention and ensuing conversation predicted event memory accuracy. Inconsistent flashbulb memories were more likely to be repeated rather than corrected over the 10-year period; inaccurate event memories, however, were more likely to be corrected. The findings suggest that even traumatic memories and those implicated in a community's collective identity may be inconsistent over time and these inconsistencies can persist without the corrective force of external influences.This is the author accepted manuscript. The final version is available from the American Psychological Association via http://dx.doi.org/10.1037/xge000005