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1)Let A, B, C, D be a Banach algebras, and U be a free ultrafilter. Can we see that ultrapowers of \begin{pmatrix} A & B \\ C & D \end{pmatrix} equal to \begin{pmatrix} (A)_U & (B)_U \\ (C)_U & (D)_U \end{pmatrix}

Albert harold
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    This question appears to be off-topic because it is too basic. See Heinrich's paper or Defant-Floret –  Nov 26 '13 at 13:47
  • Thanks. I saw them, but I didn't see anything about matrices. But they were useful for Hilbert spaces. –  Nov 27 '13 at 08:21

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