public bool Contains(HistoryItem <T> item) => this.list.Contains(item);
bool ICollection <HistoryItem <T> > .Remove(HistoryItem <T> item) => throw new NotSupportedException();
/// <summary> /// Indicates whether the current object is equal to another object of the same type. /// </summary> /// <param name="other">An object to compare with this object.</param> /// <returns>true if the current object is equal to the other parameter; otherwise, false.</returns> public abstract bool Equals(HistoryItem <T> other);
