internal static RedBlackNode Replace(System.Collections.IComparer comp, RedBlackNode t, object key, object val)
{
int c = comp.Compare(key, t.Key);
return(t.Replace(t.Key,
c == 0 ? val : t.Value,
c < 0 ? Replace(comp, t.Left, key, val) : t.Left,
c > 0 ? Replace(comp, t.Right, key, val) : t.Right));
}