The Man Who Knew InfinityOld Books In 1913, a young unschooled Indian clerk wrote a letter to G H Hardy, begging the pre eminent English mathematician's opinion on several ideas he had about numbers. Realising the letter was the work of a genius, Hardy arranged for Srinivasa Ramanujan to come to England. Thus began one of the most improbable and productive collaborations ever chronicled. With a passion for rich and evocative detail, Robert Kanigel takes us from the temples