public static Set <T> addOrUpdate <T>(Set <T> set, T value) => set.AddOrUpdate(value);
public static Set <OrdT, T> addOrUpdate <OrdT, T>(Set <OrdT, T> set, T value) where OrdT : struct, Ord <T> => set.AddOrUpdate(value);
public static Set <T> addOrUpdate <T>(Set <T> set, T value) => set.AddOrUpdate(value);
public static Set <OrdT, T> addOrUpdate <OrdT, T>(Set <OrdT, T> set, T value) where OrdT : struct, Ord <T> => set.AddOrUpdate(value);