colour n=9 k=6: vars=4608 clauses=37028 partitions=20648 -> UNSAT (0.2s)
colour n=9 k=7: vars=4608 clauses=37310 partitions=21110 -> UNSAT (0.2s)
colour n=9 k=8: vars=4608 clauses=37283 partitions=21146 -> UNSAT (0.2s)
