"But—?"
"Easy. Easy. The output from the upper generator creates negative space. But before it can establish an expanding field, the output of the lower generator nullifies it. For the lower generator is making a field of positive space equal to the force from above. Take unity. Add unity and you have two. Cancel one unity and you have unity—plus a spacedriver!"
Thirty thousand light years away, a recorder wiggled, a bell rang, and a sentient creature came out of a quiet complacence with a roar. Then came the clangor of a huge alarm and other creatures came tumbling into the huge room. They watched the recorder anxiously; then as it levelled off they left, slowly. Six remained; the others got into a small spacecraft and took off. There would be no nova for the suppression squad to extinguish; all that was needed was for the safety squad to go there and teach newcomers how not to play with fire.