Title: ON THE STUDY OF COMPLEMENTARITY PROBLEMS BY LERAY- SCHAUDER TYPE ALTERNATIVES

In this talk we will present a new topological method introduced recently in Complementarity Theory. This method is based on the concept of "exceptional family of elements" for a mapping. This concept is supported by Leray- Schauder type alternatives, or by the topological degree. We will present new results obtained in Complementarity Theory by this method . Some open problems will be also presented.