Class Vector

Vector in 3D space

Constructor:

- Vector(|x|, |y|, |z|)   (from three coordinates)
- Vector(|coordinates|)   (from any sequence containing three coordinates)

Vectors support the usual arithmetic operations
('v1', 'v2': vectors, 's': scalar): 

-  'v1+v2'           (addition)
-  'v1-v2'           (subtraction)
-  'v1*v2'           (scalar product)
-  's*v1', 'v1*s'    (multiplication with a scalar)
-  'v1/s'            (division by a scalar)

The three coordinates can be extracted by indexing.

Vectors are *immutable*, i.e. their elements cannot be changed.

Vector elements can be any objects on which the standard
arithmetic operations plus the functions sqrt and arccos are defined.