2.1 Null models
  2.1.1 Null-models of node and layer activity
 2.2 Growing multiplex networks
  2.2.1 Linear preferential attachment
  2.2.2 Non-linear preferential attachment
  2.2.3 Utilities
 2.3 Multiplex networks with inter-layer degree correlations
  2.3.1 Models based on simulated annealing