This page explains the notation and coding we are using on this site compared with writers on the subject.
this site  Doran/Lasenby  Dorst/Fontijne/Mann  

e1+e2 point at infinity 
n_{∞} 
n  ∞  
e1e2 origin point 
n_{0}  n (the bar is really on the top but this is easier in html) 
2 o  
representation of point as null vector 
X = x²n_{∞}+2xn_{0}  X = x² n + 2 x n  p=o + p + ½ p² ∞  
normalisation  n•n_{0}= 2  n•n = 2  ∞•p = 1  
see note 2 at bottom of page 360 

