I have a question about my Physics Stack Exchange post: Shankar Quantum Mechanics: Proof Inverse Of Operators
I don't get why my question was flagged as homework plus a down-vote. It is not meant as homework. Also, that line beneath the imgur link was my (poorly?) proof, In the footnote: they said: see for the concepts at the end of Theorem A.1.1. There, the proof was also one line. So what I did was simply switched the symbols and asking if its a valid proof.