Abstract :
Let ∑ be a finite alphabet and ∑* the set of all finite words (sequences of symbols) over ∑. A fuzzy event f is a mapping from ∑* into [0, 1] and is called probabilistic if it is induced by a probabilistic automaton.1Some operations are defined on fuzzy events f, g, r: for x∈∑* (f ∨ g)(x) =Max (f(x), g(x)); (f ∧ g)(x)= min (f(x), g(x)); f(x)= 1-f(x); fT(x) =f(xT) where xT= σk⋯ σ1if x = σ1⋯ σk; [f, g:r](x)= f(x)r(x)+g(x)r̄(x), etc., and the closure of the events with regard to those operations are studied. Typical results: probabilistic events are closed under the bar operation, the bracket operation, and the "T" operation, but are not closed under the "∨" or "∧" operations (except for some restricted cases). Of particular interest is the result about the T-closure, as this problem has been open for a couple of years.
