(Stallings 1970, pp. 124–128). See in particular Groups of cohomological dimension one, p. 126, at Google Books. Stallings, John (1970), "Groups of cohomological dimension one", Applications of Categorical Algebra (Proc. Sympos. Pure Math., Vol. XVIII, New York, 1968), Providence, R.I.: Amer. Math. Soc., pp. 124–128, MR0255689
(Stallings 1970, pp. 124–128). See in particular Groups of cohomological dimension one, p. 126, at Google Books. Stallings, John (1970), "Groups of cohomological dimension one", Applications of Categorical Algebra (Proc. Sympos. Pure Math., Vol. XVIII, New York, 1968), Providence, R.I.: Amer. Math. Soc., pp. 124–128, MR0255689
(Lajoie & Mura 2000, pp. 29–33). Lajoie, Caroline; Mura, Roberta (November 2000), "What's in a name? A learning difficulty in connection with cyclic groups", For the Learning of Mathematics, 20 (3): 29–33, JSTOR40248334