public int LastIndexOf(RelationalListPair <T1, T2> item) => LastIndexOf(item.X, item.Y);
public bool Contains(RelationalListPair <T1, T2> item) => Contains(item.X, item.Y);
public void Remove(RelationalListPair <T1, T2> item) { Remove(item.X, item.Y); }
public void Insert(RelationalListPair <T1, T2> item, int index) { Insert(item.X, item.Y, index); }
public void Add(RelationalListPair <T1, T2> item) { Add(item.X, item.Y); }