Hi I'm trying to learn how to load a .obj file using OpenTK in windows Forms. I have seen a lot of examples out there, but I do see almost everyone uses List, and Point[]. Code example show these highlighted like there IDE know what these are; for example

List<Tri> tris = new List<Tri>();  

but mine just returns "The type or namespace name 'Tri' could not be found" is there an include I need to add or a using I am missing. Currently have this

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Drawing;
using OpenTK;
using OpenTK.Graphics;
using OpenTK.Graphics.OpenGL;