Long long ago, there was a world of triangles. A smart guy in that world invented a camera, whose viewfinder was a
triangle. The camera's visual range could be represented by three RAYS. As the figure shows, the camera's visual
range could be represented by three rays OA, OB, OC. Note that the visual range is INFINITE.
Now, we have a camera with known visual range and a triangle DEF in the space. The inventor wants to know if the
camera can see the triangle, in other words, if there is at least one point of the triangle strict in the visual range.