Isomorphism theorems

Group isomorphism theorems

The isomorphism theorems for modules are expressed as follows

First isomorphism theorem

Let 𝜑 :𝐺 →𝐻 be a module homomorphism. Then the quotient by the kernel is isomorphic to the image: #m/thm/group

𝐺ker⁡𝜑≅im⁡𝜑≤𝐻

Second isomorphism theorem

Let 𝐴,𝐵 ≤𝐺. Then #m/thm/group

𝐴+𝐵𝐵≅𝐴𝐴∩𝐵

Third isomorphism theorem

Let 𝐴 ≤𝐵 ≤𝐺. Then 𝐵/𝐴 ≤𝐺/𝐴 and #m/thm/group

𝐺/𝐴𝐵/𝐴≅𝐺𝐵


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