In this paper, we study the properties of flexible queries in the OLAP (On-Line Analytical Processing) framework, focusing on unary operators. For this purpose, we consider the model we have defined for fuzzy multidimensional databases. This model provides means to handle fuzzy data and flexible queries. The operators defined in this model are closed on the set of fuzzy hypercubes (hereafter cubes), which means that the result of each operator on a fuzzy cube is a cube. Thus, these operators can be nested into expressions. In this paper, the combination of several queries is investigated in order to study the possibility for the definition of an algebra to manipulate fuzzy cubes. This would provide a framework for query rewriting and, as a result, for query optimization.