code: func (mn *mocknet) linksMapGet(p1, p2 peer.ID) map[*link]struct{} {
  
  	l1, found := mn.links[p1]
  	if !found {
  		mn.links[p1] = map[peer.ID]map[*link]struct{}{}
  		l1 = mn.links[p1] // so we make sure it's there.
  	}
  
  	l2, found := l1[p2]
  	if !found {
  		m := map[*link]struct{}{}
  		l1[p2] = m
  		l2 = l1[p2]
  	}
  
  	return l2
  }
docs: // get from the links map. and lazily contruct.