Voskoglou, Michael G.2011-02-182011-02-182000-011647-662Xhttp://hdl.handle.net/10400.19/930There are often situations in real life in which definitions do not have clear boundaries; for example this happens when we speak about the "long rivers" or "high mountains" of a country, about the "young people" of a town, about the "tall pupils" of a school, e.t.c.. The fuzzy sets theory was created in response to the need to have a mathematical representation of such kind of situations. Let U denote the universal set of the discourse. Then a fuzzy set A in U, initiated by Zadeh [7], is defined by means of the membership function mA, which assigns to each element of U a real value from the interval [0,1]. More specifically A = {(x,mA(x)) : x Є U} , where mA U ----> [0,1).engEnsino da Matemáticajournal article