For a long while after David Foster Wallace’s death, his widow Karen Green couldn’t make any art at all, wondered if she ever would again, but eventually, tentatively, she developed the idea for her conciliatory Heath-Robinson. “The forgiveness machine was seven-feet long,” she says, “with lots of weird plastic bits and pieces. Heavy as hell.” The idea was that you wrote down the thing that you wanted to forgive, or to be forgiven for, and a vacuum sucked your piece of paper in one end. At the other it was shredded, and hey presto.