public void Add_PowerFunction_To_Summand(double a, double b, int n, int m)
{
if (All_Functions.Multiplicands == null)
All_Functions.Multiplicands = new List<IElementaryFunction>();
All_Functions.Multiplicands.Add(new PowerFunction { Aparam = a, Bparam = b, PowerNumerator = n, PowerDenominator = m });
}