The value returned is a vector *v* of vectors of exact nonnegative
integers.
The vectors of integers *v(i)* represent the set of points near
the *i*th point.
If the point *(x(i),y(i),z(i))* is within distance *d* of
*(x(j),y(j),z(j))*, then *i* will appear in *v(j)* and
*j* will appear in *v(i)*.
A point is never in its own set of neighbours.

Sat May 8 16:42:57 EDT 1999