Finally, let’s examine more details about the “Out” triangles.
Out(Cone A, Roof* A) is the set of all the slant triangles above Roof* A.
As shown on the right, Out(Cone A, Roof* A) consists of slant triangles whose vertices are on or above the surface of Roof* A.
For example, the left figure (of the figure ) shows the third triangle (colored red) from the top, whose top and bottom vertices are on the surface and the other is above the surface.
The middle figure shows the second triangle from the top, whose second vertex is on the surface and the others are above the surface.
The right figure shows the top triangle, whose bottom vertex is on the surface and the others are above the surface.