`ivs`

finds all independent vertex sets in the
network, obeying the size limitations given in the `min`

and `max`

arguments.

`largest_ivs`

finds the largest independent vertex
sets in the graph. An independent vertex set is largest if there is no
independent vertex set with more vertices.

`maximal_ivs`

finds the maximal independent vertex
sets in the graph. An independent vertex set is maximal if it cannot be
extended to a larger independent vertex set. The largest independent vertex
sets are maximal, but the opposite is not always true.

`independece.number`

calculate the size of the largest independent
vertex set(s).

These functions use the algorithm described by Tsukiyama et al., see
reference below.