Second-Order Optimality Conditions for a Class of Quasidifferentiable Functions

Let f:R~n→R be continuously quasidifferentiable.Definition I The upper and lower.second-order d-directional derivativesof f at x are defined,respectively,by f”_+(x,v,d):(?)〈v_k+v_k-v,x_k-x〉/t_k~2,f”_(-)(x,v,d):(?)〈v_k+v_k-v,x_k-x〉/t_k~2,where(i)t_k>0,x_k→x;(ii)(x_k-x)/t_k→d;(iii)v_k+v_k→v,v_k∈(?)f(x_k),(?)∈(?)f(x_k).