Hollings, Christopher (2014), "Section 12.3: Czechoslovakia, 1968, and Semigroup Forum", Mathematics across the Iron Curtain, History of Mathematics, vol. 41, Providence, RI: American Mathematical Society, pp. 326–332, ISBN978-1-4704-1493-1, MR3222721.
Lawson, Jimmie D. (2002), "An interview with Karl H. Hofmann on the occasion of his seventieth birthday", Semigroup Forum, 65 (3): 317–328, doi:10.1007/s002330010146, MR1930163. As quoted by Hollings (2014).
Hofmann, Karl H. (1995), "From a topological theory of semigroups to a geometric one", Semigroup Forum, 50 (1): 123–134, doi:10.1007/BF02573511, MR1301557. As quoted by Hollings (2014).
doi.org
Lawson, Jimmie D. (2002), "An interview with Karl H. Hofmann on the occasion of his seventieth birthday", Semigroup Forum, 65 (3): 317–328, doi:10.1007/s002330010146, MR1930163. As quoted by Hollings (2014).
Hofmann, Karl H. (1995), "From a topological theory of semigroups to a geometric one", Semigroup Forum, 50 (1): 123–134, doi:10.1007/BF02573511, MR1301557. As quoted by Hollings (2014).