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Bibliography

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R. Bott and H. Samelson, On the Pontryagin product in spaces of paths, Comment. Math. Helv. 27 (1953), 320-337. MR 0060233 (15:643b)

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B. Eckmann and P. J. Hilton, Group-like structures in general categories. I, Math. Ann. 145 (1962), 227-255; II, ibid. 151 (1963), 150-186; III, ibid. 150 (1963), 165-187.

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-, Structure maps in group theory, Fund. Math. 50 (1961/62), 207-221. MR 0132776 (24:A2612)

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D. M. Kan, On monoids and their dual, Bol. Soc. Mat. Mexicana (2) 3 (1958), 52-61. MR 0111035 (22:1900)

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-, A combinatorial definition of homotopy groups, Ann. of Math (2) 67 (1958), 282-312. MR 0111032 (22:1897)