 
 
 
13.5.4  Vectors in space: vector
See section 12.7.4 for vectors in the plane.
The vector command returns and draws vectors, given
one of the following types of arguments:
- 
A list of the coordinates of a vector. The vector is drawn
beginning at the origin.
 Input:
vector([1,2,3])
 Output:
- Two points or two lists of coordinates for points.
 The vector is drawn from the first point to the second.
 Input:
vector(point(-1,0,0),point(0,1,2))
 or:
vector([-1,0,0],[0,1,2])
 Output:
- A point and a vector.
 The vector is drawn beginning at the point.
 Input:
V := vector([-1,0,0],[0,1,2])
 then:
vector(point(-1,2,0),V)
 Output:
 
 
