n=7 k=2 b=None: COL_k holds for all star-free systems (UNSAT after 32 refinements, 0.0s)
n=7 k=3 b=None: COL_k holds for all star-free systems (UNSAT after 93 refinements, 0.1s)
n=7 k=4 b=None: COL_k holds for all star-free systems (UNSAT after 124 refinements, 0.2s)
n=8 k=2 b=None: COL_k holds for all star-free systems (UNSAT after 68 refinements, 0.7s)
  ... 200 refinements, 0.9s
n=8 k=3 b=None: COL_k holds for all star-free systems (UNSAT after 220 refinements, 2.9s)
  ... 200 refinements, 1.4s
n=8 k=4 b=None: COL_k holds for all star-free systems (UNSAT after 289 refinements, 2.7s)
