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Counterexample

Is this true?

Real matrix diagonalisable over C⇒\mathbb{C} \Rightarrow diagonalisable over R\mathbb{R}

No — it is false.

The counterexample

The object that kills this claim comes with Trap Analysis.

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86 counterexamples are free — including most of the ones Part C leans on hardest.

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Invariants don't determine

Two objects sharing an invariant were treated as the same object.

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linear algebra

Go deeper· Explained in full in Diagonalisability — the criteria card· Asked in CSIR NET December 2025· From Eigenvalues and Canonical Forms › Diagonalisability criteria

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