The question is in the title, in Rotman's "An introduction to homological algebra", page 125 is the next proposition:
After the diagram, it says that $R/I$ is cyclic, why ?
The question is in the title, in Rotman's "An introduction to homological algebra", page 125 is the next proposition:
After the diagram, it says that $R/I$ is cyclic, why ?
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Because it is generated by $1+I$.