"The date ... is usually assumed to be about 350 B.C., but . . . it is perhaps safer to say that he lived after, and perhaps soon after, 500 B.C.": A. A. MacDonell, India's Past: A Survey of Her Literatures, Religions, Languages and Antiquities (Oxonii: Oxford University Press, 1927) pp. 136-137 (Paginae selectae apud Google Books)
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Paul Thieme, recensio operis The Sanskrit Language T. Burrow in Language vol. 31 (1955) pp. 428-448 ad p. 429 JSTOR[nexus deficit]