private void BtnResolve_Click(object obj)
        {
            Result = string.Empty;
            if (_forest == null)
            {
                return;
            }
            IItemNumerical item = _forest.CreateItem();
            int            i    = 0;

            foreach (NameValue nv in NameValueList)
            {
                item.SetValue(nv.Name, nv.Value);
                i++;
            }
            if (i == 0)
            {
                return;
            }
            double res = _forest.Resolve(item);

            Result = res.ToString();
        }