theories.group_theory
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Group theory (especially finite group theory).

[subgroup](subgroup.lean) : general subgroup theories, quotient group using quot

[finsubg](finsubg.lean)   : finite subgroups (finset and fintype), Lagrange theorem, finite cosets and lcoset_type, normalizer for finite groups, coset product and quotient group based on lcoset_type, semidirect product

[hom](hom.lean) 	  : homomorphism and isomorphism, kernel, first isomorphism theorem

[perm](perm.lean)	  : permutation group

[cyclic](cyclic.lean)	  : cyclic subgroup, finite generator, order of generator, sequence and rotation

[action](action.lean)	  : fixed point, action, stabilizer, orbit stabilizer theorem, orbit partition, Cayley theorem, action on lcoset, cardinality of permutation group

[pgroup](pgroup.lean)	  : subgroup with order of prime power, Cauchy theorem, first Sylow theorem