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Published online by Cambridge University Press: 20 April 2023
We show that Katětov and Rudin–Blass orders on summable tall ideals coincide. We prove that Katětov order on summable tall ideals is Galois–Tukey equivalent to  $(\omega ^\omega ,\le ^*)$. It follows that Katětov order on summable tall ideals is upwards directed which answers a question of Minami and Sakai. In addition, we prove that
$(\omega ^\omega ,\le ^*)$. It follows that Katětov order on summable tall ideals is upwards directed which answers a question of Minami and Sakai. In addition, we prove that  ${l_\infty }$ is Borel bireducible to an equivalence relation induced by Katětov order on summable tall ideals.
${l_\infty }$ is Borel bireducible to an equivalence relation induced by Katětov order on summable tall ideals.
 ${F}_{\sigma }$
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 Fundamenta Mathematicae, vol. 138 (1991), no. 2, pp. 103–111.CrossRefGoogle Scholar
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 Fundamenta Mathematicae, vol. 138 (1991), no. 2, pp. 103–111.CrossRefGoogle Scholar ${F}_{\sigma }$
-ideals. Archive for Mathematical Logic, vol. 55 (2016), pp. 883–898.CrossRefGoogle Scholar
${F}_{\sigma }$
-ideals. Archive for Mathematical Logic, vol. 55 (2016), pp. 883–898.CrossRefGoogle Scholar