Plofker, Kim (2007). Mathematics in India. p. 17. ISBN978-0691120676.. In relative chronology, they predate Āpastamba, which is dated by Robert Lingat to the sutra period proper, between c. 500 to 200 BCE. Robert Lingat, The Classical Law of India, (Munshiram Manoharlal Publishers Pvt Ltd, 1993), p. 20