The distribution function of a random vector \((\xi, \eta)\) is of the form:

(a) \(F(x, y)=F_{1}(x) F_{2}(y)+F_{3}(x)\);

(b) \(F(x, y)=F_{1}(x) F_{2}(y)+F_{3}(x)+F_{4}(y)\).

Can the functions \(F_{3}(x)\) and \(F_{4}(x)\) be arbitrary? Are the components of the vector \((\xi, \eta\) ) dependent or independent?