The "Nyaya-sutras" is attributed to Gautama, who was at least the principal author. According to Karl Potter, this name has been a very common Indian name, and the author is also reverentially referred to as Gotama, Dirghatapas and Aksapada Gautama. Little is known about Gautama, or which century he lived in. Scholarly estimates, based on textual analysis, vary from the 6th century BCE, making him a contemporary of Buddha and Mahavira, to as late as the 2nd century CE. Some scholars favor the theory that the cryptic text Nyaya-sutras was expanded over time by multiple authors, with the earliest layer from about mid-first millennium BCE that was composed by Gautama. The earliest layer is likely to be Book 1 and 5 of the text, while Book 3 and 4 may have been added last, but this is not certain.