See, for example, Gołab 1939. Gołab, St. (1939). "Über den Begriff der "Pseudogruppe von Transformationen"". Mathematische Annalen (in German). 116: 768–780. doi:10.1007/BF01597390.
Gonçalves, D; Sobottka, M; Starling, C (2017). "Inverse semigroup shifts over countable alphabets". Semigroup Forum. 96 (2): 203–240. arXiv:1510.04117. doi:10.1007/s00233-017-9858-5Corollary 4.9{{cite journal}}: CS1 maint: postscript (link)
Howie 1995, Theorem 5.9.2. Originally, McAlister 1974a,b. Howie, J. M. (1995). Fundamentals of Semigroup Theory. Oxford: Clarendon Press. ISBN0198511949. McAlister, D. B. (1974a). "Groups, semilattices and inverse semigroups". Transactions of the American Mathematical Society. 192: 227–244. doi:10.2307/1996831. JSTOR1996831.
Howie 1995, Theorem 5.9.2. Originally, McAlister 1974a,b. Howie, J. M. (1995). Fundamentals of Semigroup Theory. Oxford: Clarendon Press. ISBN0198511949. McAlister, D. B. (1974a). "Groups, semilattices and inverse semigroups". Transactions of the American Mathematical Society. 192: 227–244. doi:10.2307/1996831. JSTOR1996831.
First a short announcement in Wagner 1952, then a much more comprehensive exposition in Wagner 1953. Wagner, V. V. (1952). "Generalised groups". Proceedings of the USSR Academy of Sciences (in Russian). 84: 1119–1122. English translation(PDF) Wagner, V. V. (1953). "The theory of generalised heaps and generalised groups". Matematicheskii Sbornik. Novaya Seriya (in Russian). 32 (74): 545–632.