The setting of entropy was statistical mechanics: in [1] Shannon introduced entropy of a partition of a set, linked to a probability measure.

Now, we recall this definition. Let be an abstract space, a -algebra of subsets of and a probability measure defined on. Moreover is the collection of the partition, where

Basic notions and notations can be found in [2] . Setting with (complete system),

Shannon’s entropy is

and it is measure of uncertainty of the system. Shannon’s entropy is the weight arithmetic mean, where the weights are. Many authors have studied this entropy and its properties, for example: J. Aczél, Daróczy, C. T. Ny; for the bibliography we refer to [3] [4] .

Another entropy was introduced by Rényi, called entropy of order,:

and it was used in many problems [5] [6] .

In generalizing Bolzmann-Gibbs statistical mechanics, Tsallis’s entropy was introduced [7] :

We note that all entropies above are defined through a probability measure.

In 1967 J. Kampé de Feriét and B. Forte gave a new definition of information for a crisp event, from axiomatic point of view, without using probability [8] -[10] . Following this theory other authors have presented measures of information for an event [11] . In [12] , with Benvenuti we have introduced the measure of information for fuzzy sets [13] [14] without any probability or fuzzy measure.

In this paper we propose a class of measure for the entropy of an information for a crisp or fuzzy event, without using any probability or fuzzy measure.

We think that not using probability measure or fuzzy measure in the definition of entropy of the information of an event, can be an useful generalization in the applications in which probablility is not known.

So, in this note, we use the theory explained by Khinchin in [15] and we give a new definition of entropy of information of an event. In this way it is possible to measure the unavailability of information.

The paper is organized as follows. In Section 2 there are some preliminaries about general information for crisp and fuzzy sets. The definitions of entropy and its measure are presented in Section 3. Section 4 is devoted to an application. The conclusion is considered in Section 5.

Let be an abstract space and the -algebra of crisp sets General information for crisp sets [8] [10] is a mapping

such that:

1)

2),

In analogous way [12] , the definition of measure of general information was introduced by Benvenuti and ourselves for fuzzy sets. Let be an abstract space and the -algebra of fuzzy sets. General information is a mapping

such that:

1)

2),

Using general information recalled in Section 2, in this paragraph a new form of information entropy will be introduced, which will be called general information entropy. Information entropy means the measure of un- availability of a given information.

In this paragraph, an application of information entropy will be indicated: it concerns the value of information entropy for the union of two disjoint crisp sets. The procedure of solving this problem is the following: first, the presentation of the properties, second the translation of these properties in functional equations, by doing so, it will be possible to solve these systems [16] .

It is possible to extend this application also to the union of two disjoint fuzzy sets.

On crisp setting as in Section 2, let and two disjoint sets. In order to characterize information entropy of the union, the properties of this operation are used. The approach is axiomatic. The properties used by us are classical:

(u₃) as and,

Information entropy of the union is supposed to be dependent on and

where

Setting:, , , , with the properties lead to solve the following system of functional equations:

We are looking for a continuous function as an universal law with the meaning that the equations and the inequality of the system must be satisfied for all variables on every abstract space satisfying to all restrictions.

Proposition 4.1. A class of the solutions of the system is

where is any continuous bijective and strictly decreasing function with and

Proof. The proof is based on the application of the theorem of Cho-Hsing Ling [17] about the representation of associative and commutative function with the right element (here it is) as unit element.

From (1) and (2) information entropy of the union of two disjoint set is expressed by

where is any continuous bijective and strictly decreasing function with and

By axiomatic way, a new form of information entropy has been introduced using information theory without probability given by J. Kampé De Fériet and Forte. For this measure of information entropy, called by us, general because it doesn’t contain any probability or fuzzy measure, it has been given a class of measure for the union of two crisp disjoint sets.

This research was supported by research center CRITEVAT of “Sapienza” University of Roma and GNFM of MIUR (Italy).