public class InterpolationLagrange
        {
            public Func<double, double> L_x = x => 0;

            public InterpolationLagrange(double[] X_arr, double[] Y_arr)
            {
                int numIndex;
                double[] X_cut;
                Func<double, double> L_x2;
                for (int i = 0; i < X_arr.Count(); i++)
                {
                    numIndex = Array.IndexOf(X_arr, X_arr[i]);
                    X_cut = X_arr.Where((val, idx) => idx != numIndex).ToArray();
                    double Y_b = Y_arr[i];
                    double X_b = X_arr[i];
                    L_x2 = x => Y_b * get_l_i(X_b, X_cut)(x);
                    L_x = x => L_x(x) + L_x2(x);
                }
            }

            public Func<double, double> get_l_i(double x_li, double[] x_arr)
            {
                Func<double, double> l_i = x => x;
                foreach (double x_i in x_arr)
                {
                    l_i = x => l_i(x) * (x - x_i) / (x_li - x_i);
                }
                return l_i;
            }
        }

L_x = x => L_x(x) + L_x2(x);

            Func<int> x = () => 1;
            x = () => x();
            var result = x();