code: @Pure
  	public N getChildAt(IcosepOctTreeZone zone) {
  		if (zone == IcosepOctTreeZone.ICOSEP) {
  			return this.nicosep;
  		}
  		return getChildAt(zone.toOctTreeZone());
  	}
docs: Replies the node that is corresponding to the given zone.
  
  @param zone the zone.
  @return the child node for the given zone, or <code>null</code>