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A Banach Space $X$, $A,B$ are operators on $X$ where $AB$ is invertible but $A$ or $B$ is not invertible.
For finite dimensional case we know that result so the example will come from infinite dimension.
Thank You.
2026-03-26 17:52:30.1774547550
$AB$ is invertible but $A$ or $B$ is not invertible.
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