Ronald O’Brien sat staring at the screen of his computer, elbows on the desk, his cheeks propped in his hands, the very image of a blocked writer. He sighed, and stretched with relief when his son entered. Unlike some, he had no rules about not being disturbed during working hours. His son John recognised the attitude. He came over and placed a hand on his father’s shoulder. “Not coming?” he asked sympathetically. “No.” “What is it? Talking about it might help.” “It’s a counter-factual, beginning just after Columbus’s first voyage.” “Yes?” “Columbus has returned, and reported to the Spanish Court.…