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Let $R$ be a ring with identity $e$, $A, B\in R$, $A\neq 0$, $B$ is invertible element. If $A\cdot B = A$ then $B = e$.
Let $R$ be a ring with identity $e$, $A, B\in R$, $B$ is invertible element. If $A\cdot B = A$ then $B = e$.
Let $R$ be a ring with identity $e$, $A, B\in R$. If $A\cdot B = A$ then $B = e$.