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eby justrather than in group theory. Semigroups shouPositive integegative inte role of bijections from group theoryons do not imitate any semigrouonoid thing in group theory though. A deep result in the classificat are a generalization of groups in a different direction; thlace thenon-em semigroups like Gras been of particular importance in theoretical computer science since the 1950easilion

Other fundamental techniques of studyingment.