### 12.3.1 Draw unit vectors:
Ox_3d_unit_vector
Oy_3d_unit_vector
Oz_3d_unit_vector
frame_3d

The Ox_3d_unit_vector command draws the unit vector in
the x-direction on a three-dimensional graphic screen.

Input:

Ox_3d_unit_vector()

Output:

Similarly, the Oy_3d_unit_vector and
Oz_3d_unit_vector commands draw the unit vector in the y
and z directions, respectively.

These commands have no parameters, but can be decorated with the
legend command.

Input:

Ox_3d_unit_vector(), legend(point([1,0,0]),"unit x vector",blue)

Output:

The frame_3d command draws all three vectors simultaneously.