A unique aspect of sponsored search advertising is that it allows firms to track what products consumers initially search for and what products they eventually buy after visiting their website – something that is typically hard to acquire in physical world settings. Based on a unique dataset that contains information on what keyword advertisements induced consumers to arrive on a firm’s website...

in this paper, we formalize the menger probabilistic normed space as a category in which its objects are the menger probabilistic normed spaces and its morphisms are fuzzy continuous operators. then, we show that the category of probabilistic normed spaces is isomorphicly a subcategory of the category of topological vector spaces. so, we can easily apply the results of topological vector spaces...

The notion of approximation problems was formally introduced by Johnson [3] in his pioneering paper on the approximation of combinatorial optimization problems, and it was also suggested a possible classification of optimization problems on grounds of their approximability properties. Since then, it was clear that, even though the decision versions of most NP-hard optimization problems are poly...