public void InterfaceProp_VsClass()
{
Person iP = new Person {
Sex = Sex.Male
};
IPeselPersonalData iPPD = iP;
iPPD.Sex = Sex.Female;
Console.WriteLine($"iP {iP.Sex}, iPPD {iPPD.Sex}");
}
public static bool IsValidPesel(this IPeselPersonalData pesel)
{
return(pesel.Sex != Sex.Undefined);
}