Find all pairs of points whose distance is at most r
Parameters :
r : positive float
The maximum distance
p : float 1<=p<=infinity
Which Minkowski norm to use
eps : nonnegative float
Approximate search. Branches of the tree are not explored
if their nearest points are further than r/(1+eps), and branches
are added in bulk if their furthest points are nearer than r*(1+eps).
Returns :
results : set
set of pairs (i,j), i<j, for which the corresponing positions are
close.