We analyze a model of interactive unawareness introduced by Heifetz, Meier and Schipper. We consider two axiomatizations for their model, which capture different notions of validity. These axiomatizations allow us to compare the Heifetz et al. approach to both the standard (S5) epistemic logic and two other approaches to unawareness: that of Fagin and Halpern and that of Modica and Rustichini. We show that the differences between the Heifetz et al. approach and the others are mainly due to the notion of validity used and the fact that the Heifetz et al. approach is based on a 3-valued propositional logic.

Awareness has been shown to be a useful addition to standard epistemic logic. However, standard propositional logics for knowledge and awareness cannot express the fact that an agent knows that there are facts of which he is unaware without there being an explicit fact that the agent knows he is unaware of. We extend Fagin and Halpern's logic of general awareness to a logic that allows quantification over variables, so that there is a formula in the language that says "an agent explicitly knows that there exists a fact of which he is unaware." Moreover, that formula can be true without the agent explicitly knowing that he is unaware of any particular formula. We provide a sound and complete axiomatization of the logic. Finally, we show that the validity problem for the logic is recursively enumerable, but not decidable.

Standard game theory assumes that the structure of the game is common knowledge among players. We relax this assumption by considering extensive games where agents may be unaware of the complete structure of the game. In particular, they may not be aware of moves that they and other agents can make. We show how such games can be represented; the key idea is to describe the game from the point of view of every agent at every node of the game tree. We provide a generalization of Nash equilibrium and show that every game with awareness has a generalized Nash equilibrium.Finally, we extend these results to games with awareness of unawareness, where a player i may be aware that a player j can make moves that i is not aware of, and to subjective games, where payers may have no common knowledge regarding the actual game and their beliefs are incompatible with a common prior.

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A freqüência de infecções hematogênicas por Candida (candidemia) tem aumentado consideravelmente, especialmente em unidades de terapia intensiva e ou de assistência a pacientes críticos 2 3 4 7 8 14 15 17 20 24 . O aumento na freqüência de candidemia tem sido observado particularmente entre pacientes em uso de antibióticos, terapia imunossupressora, nutrição parenteral, e em pacientes expostos a múltiplos procedimentos invasivos 11 24 .Espécies do gênero Candida, em particular Candida albicans, têm emergido como importantes patógenos nosocomiais, estando associadas a quase 80% de todas as infecções fúngicas nosocomiais, representando a maior causa de fungemia 2 24 . Candidemia é a quarta causa mais comum de infecção na corrente sangüínea em hospitais terciários, e sua ocorrência tem sido associada à longa permanência hospitalar e alta mortalidade 5 10 18 21 . ABSTRACTWe conducted a prospective, observational, laboratory-based study on candidemia to investigate the incidence of candidemia, species distribution and clinical conditions between September 2003 and March 2004 in a private tertiary hospital in Recife, northeastern Brazil. Cases of candidemia were defined as occurrences of isolation of Candida spp from blood cultures. The incidence rate was calculated per 1,000 admissions. A total of 5,532 patients were admitted to the hospital during the study period, and 1,745 blood cultures were processed. Twenty-one episodes of candidemia were observed in 18 patients. The incidence rate of candidemia was 3.9 episodes per 1,000 admissions. Non-albicans species accounted for more than 50% of the cases, and Candida parapsilosis (33%) and Candida tropicalis (24%) predominated. Eleven (61%) patients died. The incidence of candidemia was higher than that observed in a Brazilian multicenter study. Candidemia was caused predominantly by non-albicans species.