The slide shows how flows of triangles are obtained.
First, divide facets of 3-cube [0,1]3 into triangles. As shown on the left, each facet is divided into two triangles.
Next, pile up the 3-cubes along the direction of (-1, -1, -1). That is, they are piled up from (+inf, +inf, +inf) toward (-inf, -inf, -inf). And we obtain “peaks and valleys” of 3-cubes.
Note that the division of facets makes up a division of the surface of the “peaks and valleys.”
Finally, project the surface on a hyperplane that is perpendicular to vector (-1, -1, -1).
Then, as shown on the right, we obtain a flow of triangles which is induced by the division of the surface. For example, the blue slant triangles on the “peaks and valleys” specify the blue trajectory of flat triangles on the hyperplane.