- Iwasawa group
In mathematics a group is sometimes called an Iwasawa group or M-group or modular group if its
lattice of subgroups is modular.Finite modular groups are also called Iwasawa groups, after harv|Iwasawa|1941 where they were classified. Both finite and infinite M-groups are presented in textbook form in harv|Schmidt|1994|loc=Ch. 2.4. Modern study includes harv|Zimmerman|1989. A finite "p"-group is a modular group if and only if every subgroup is permutable, by harv|Schmidt|1994|loc=Lemma 2.3.2, p. 55. Every subgroup of a finite "p"-group is subnormal, and those finite groups in which subnormality and permutability coincide are called PT-groups. In other words, a finite "p"-group is an Iwasawa group if and only if it is a PT-group.
References
*Citation | last1=Iwasawa | first1=Kenkiti | title=Über die endlichen Gruppen und die Verbände ihrer Untergruppen | id=MathSciNet | id = 0005721 | year=1941 | journal=J. Fac. Sci. Imp. Univ. Tokyo. Sect. I. | volume=4 | pages=171–199
*Citation | last1=Iwasawa | first1=Kenkiti | title=On the structure of infinite M-groups | id=MathSciNet | id = 0015118 | year=1943 | journal=Jap. J. Math. | volume=18 | pages=709–728
*Citation | last1=Schmidt | first1=Roland | title=Subgroup Lattices of Groups | publisher=Walter de Gruyter | series=Expositions in Math | isbn=978-3-11-011213-9 | id=MathSciNet|id=1292462 | year=1994 | volume=14
*Citation | last1=Zimmermann | first1=Irene | title=Submodular subgroups in finite groups | doi=10.1007/BF01221589 | id=MathSciNet | id = 1022820 | year=1989 | journal=Mathematische Zeitschrift | issn=0025-5874 | volume=202 | issue=4 | pages=545–557
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