Code to characterize H-pivot-minor-free graphs in terms of minimal forbidden induced subgraphs.

This code was used to obtain results in the paper:
"Computing Small Pivot-Minors"
by Konrad K. Dabrowski, François Dross, Jisu Jeong, Mamadou Moustapha Kanté,
O-joung Kwon, Sang-il Oum and Daniël Paulusma,
LNCS Proc. WG 2018 (to appear)

To be used with Sage version 8.2 or higher. Sage is available from http://www.sagemath.org/ 

Before using, install sortedcontainers using
   ./sage -pip install sortedcontainers

To calculate the forbidden induced subgraph characterization for
H-pivot-minor-free graphs, set input_graph to H in wg2018.sage, then run
   ./sage wg2018.sage

There are two options in the file:
1. Setting show_graph6 to True outputs the chararacterization in graph6 format
2. Setting draw_graphs to True draws the graphs

The second option only works if the code is run as part of a Sage notebook (to do this run ./sage -n ).
