Countable ordinal

A countable ordinal has a countable set as its underlying set.

These are the ordinals strictly below the first uncountable ordinal.

 Ancestors (6)

 Incoming links (18)

Countability of constructible omega-one
Countable fixed point of a normal ordinal function
Countable-ordinal correctness under constructibility
Countable rank-initial segment cannot model ZFC
First uncountable ordinal is regular
Inner models with all reals preserve omega-one
Past exam of the logic and set theory course of the University of Oxford / 2009 / B / 4 / iii / Solution
Past exam of the mathematics course of the University of Cambridge / 2012 / iii / Paper 83 / 4 / Solution
Past exam of the mathematics course of the University of Cambridge / 2014 / iii / Paper 19 / 2 / i / a / Solution
Past exam of the mathematics course of the University of Cambridge / 2017 / ii / Paper 4 / 15H / Solution
Past exam of the mathematics course of the University of Cambridge / 2018 / iii / Paper 121 / 1 / v / c / Solution
Past exam of the mathematics course of the University of Cambridge / 2018 / iii / Paper 121 / 2 / iii / Solution
Past exam of the mathematics course of the University of Cambridge / 2019 / iii / Paper 121 / 1 / ii / Solution
Past exam of the mathematics course of the University of Cambridge / 2019 / ii / Paper 3 / 16I / ii / Solution
Past exam of the mathematics course of the University of Cambridge / 2022 / ii / Paper 2 / 16F / b / iv / Solution
Past exam of the mathematics course of the University of Cambridge / 2024 / iii / Paper 128 / 1 / c / Solution
Past exam of the mathematics course of the University of Cambridge / 2025 / iii / Paper 128 / 1 / d / Solution
Well-order code

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