Rees, D. Note on semi-groups. (English) Zbl 0063.06456 Proc. Camb. Philos. Soc. 37, 434-435 (1941). Not reviewed Cited in 7 Documents PDFBibTeX XMLCite \textit{D. Rees}, Proc. Camb. Philos. Soc. 37, 434--435 (1941; Zbl 0063.06456)