Three Isomorphism Theorems
2020-2νκΈ°, λνμμ βνλλμ1β μμ μ λ£κ³ 곡λΆν λ°λ₯Ό μ 리ν κΈμ λλ€. μ§μ μ μΈμ λ νμμ λλ€ :)
μ§κΈ λ€λ£¨λ Isomorphism Theoremμ μμ ν μ΄ν΄νκ³ μ²΄λνλ€λ©΄, κ΅°λ‘ μ체λ₯Ό μμ£Ό κΉκ² μ΄ν΄ν μ μλ€ γ γ
1st Isomorphism Theorem; FHTPermalink
첫λ²μ¬ Isomorphism Theoremμ μ΄μ μ ν¬μ€νΈμμ μ΄λ―Έ λ€λ£¨μλ€. FHTκ° κ³§ 1st Isomorphism Theoremμ΄λ€!
Theorem. Fundamental Homormophism Theorem (FHT)
Let
Then,
is a group.
Lemma 34.4Permalink
Lemma.
Let
Then,
λ§μ½
μ¦λͺ μ΄ μκ°λ³΄λ€ μ½λ€!
proof.
1.
Let
Then,
λ°λλ‘
λμ μ’ ν©νλ©΄,
2.
Normal subgpκ³Ό μΌλ° subgpλ§ μλ€λ©΄,
κ°λ¨ν
(1) closed under opr
(2) identity
(3) inverse
Definition. Subgp generated by set
μ΄λ, intersection of subgpsλ μ¬μ ν subgpμ΄λΌλ κ²μ΄ μλ €μ Έ μλ€.
μ¦, set
join Permalink
Definition.
β» μ΄λ! λ§μ½
βλ§μ½
μ΄λ, μ΄μ΄ μ’μ
νμ§λ§, μμ½κ²λ
μ°λ¦¬κ° μμμ μ΄ν΄λ³Έ Lemmaλ
λ°λΌμ
2nd Isomorphism TheoremPermalink
Theorem. 2nd Isomorphism Theorem
Let
Then,
μ 리 μ체λ μ λ§ κ°κ²°νλ€β¦ νμ§λ§, λ΄μ©μ ν λ¬Έμ₯μΌλ‘ μμΆν΄ λμ κ²μ΄λΌ μ 리λ₯Ό μ λνλ λ°κΉμ§ νμν λ·λ°°κ²½μ΄ λ§μ νΈμ΄λ€ γ γ
proof.
λ¨Όμ κ°μ μΈ
Normal subgpμ λν΄μ μλμ λͺ μ κ° μ±λ¦½νλ€.
λͺ μ μ μ¦λͺ μ κ°λ¨νλ μ¬κΈ°μμλ μ-λ΅ νλ€.
μ΄λ,
μ΄λ²μλ λνμμ μ°λ³μΈ
λ§μ½
λ°λΌμ
λλμ΄ μ¦λͺ μ λ³Έκ²μμ΄λ€!
μλμ κ°μ homomorphism
μ΄λ,
λν,
μ΄μ μ΄ homo-
μ°λ¦¬λ
λ°λΌμ
λ°λλ‘,
λ°λΌμ
λ°λΌμ
FHTμ μν΄
λ°λΌμ
3rd Isomorphism TheoremPermalink
Theorem. 3rd Isomorphism Theorem
Let
Then,
μ λ κ³Όμ μ체λ 2nd iso- theoremμ λΉν΄μ μ λ§ μ¬μ΄ νΈμ΄λ€ γ γ
proof.
Define a homomoprhism
Then, check properties of
(1) well-defined
Supp.
(2)
clear
(3)
λ°λΌμ
FHTμ μν΄
μ΄λ,
λ°λΌμ
λ°λλ‘
λ°λΌμ
λ°λΌμ
λ€μ FHTμ μν΄
λλμ΄ Isomorphism Thm κΉμ§ λλ¬νλ€!!
μμΌλ‘λ κ΅°λ‘ μ λ€μν μ 리λ€κ³Ό μ¬λ‘λ€μ΄ κΈ°λ€λ¦¬κ³ μμΌλ! κΈ°λνμλΌ!!!
