def normal
      vec1 = self.vertices[1] - self.vertices[0]
      vec2 = self.vertices[2] - self.vertices[0]
      return (vec1.cross(vec2).normalize)
    end
def normal
      vec1 = self.vertices[1] - self.vertices[0]
      vec2 = self.vertices[2] - self.vertices[0]
      return (vec1.cross(vec2).normalize)
    end
[Output]
  return normal vector as Vector3.