 
introduces a direction d initialised with the
direction of vector $$v.
 
 
introduces the direction d of line $$l.
 
 
introduces the direction d of ray $$r.
 
 
introduces the direction d of segment $$s.
 
 
introduces a direction d initialised with the direction
from the origin to the point with Cartesian coordinates $$(x, y, z).



returns values, such that d== Direction_3<Kernel>(delta(0),delta(1),delta(2)). Precondition: : $$0 i 2. 

 returns delta(0). 

 returns delta(1). 

 returns delta(2). 

 
Test for equality.  

 
Test for inequality.  
 
 The direction opposite to d.  

 returns a vector that has the same direction as d. 
 
 
returns the direction obtained by applying $$t on d. 