Lehmann (1995), p. 165. Lehmann, Joel (1995). "Converging Concepts of Series: Learning from History". In Swetz, Frank; Fauvel, John; Bekken, Otto; Johansson, Bengt; Katz, Victor (eds.). Learn from the Masters!(PDF). Mathematical Association of America. pp. 161–180.
Lehmann (1995), p. 176. Lehmann, Joel (1995). "Converging Concepts of Series: Learning from History". In Swetz, Frank; Fauvel, John; Bekken, Otto; Johansson, Bengt; Katz, Victor (eds.). Learn from the Masters!(PDF). Mathematical Association of America. pp. 161–180.