The exact narration is implemented, with all the specified
optimisations.

- neighbour creation is delayed;
- if multiple PCs are found, only the first one is processed, the
  remaining ones are be silently ignored;
- a node ignores all challenge requests contained in a packet except
  the last one;
- and it ignores a challenge request in the case where it is contained
  in a packet with an Index that matches the one in the Neighbour Table
  and a PC that is smaller or equal to the one contained in the
  Neighbour Table.