We give a short answer to the question in the title: dendrits. Precisely we show that the C∗-algebra C(X) of all complex-valued continuous functions on a compactum X is projective in the category C of all (not necessarily commutative) unital C∗-algebras if and only if X is an absolute retract of dimension dimX ≤ 1 or, equivalently, that X is a dendrit.

The typical difficulty of various NP-hard problems varies with simple parameters describing their structure. This behavior is largely independent of the search algorithm, but depends on the choice of problem ensemble. A given problem instance belongs to many different ensembles, so applying these observations to individual problems requires identifying which ensemble is most appropriate for pre...

Dealing with user preferences is becoming a widespread issue in novel data-intensive application domains, such as electronic catalogs, e-commerce, multimedia databases, and real estates. Given a set of preferences, an important problem is to efficiently determine which are the “best” objects, according to such preferences. In this paper we assume that preferences are expressed in a qualitative ...

Let M(R) denote the measure algebra on the additive group of the reals. R. G. Douglas recently pointed out to us the importance of the following question in the study of Wiener-Hopf integral equations: if fxÇ:M(R) is invertible, then under what conditions does jit = exp(j>) for some vGM(R)? The relevance of the above question in integral equations stems from the fact that if JJLÇÏM(R) is invert...

Aspergillus fumigatus is a ubiquitous fungus that causes a variety of diseases in man and animals. A number of protein, carbohydrate, and glycoprotein antigens have been identified from A. fumigatus. The diseases are diverse, and therefore are the antigens and their roles in causing or modulating the diseases. The induction and binding of antibodies and the interaction of antigen and various im...

This paper proposes a one shot normal form game of agreement formation. It introduces a new notion of strategy, which is, for each player, to say which of the possible agreements are acceptable. Therefore, the strategy is a vector of choices. For a given strategy profile, different sizes are then acceptable and it is assumed that the largest agreement is achieved. I propose a concept of strong ...