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Pietro Majer
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To complete the preceding answerspicture (the obvious remaining part). If ${S\subset\mathbb R}$ is well ordered, then it is countable: indeed it has countable cofinality. Thus well-ordered subsets of R are exactly countable ordinals.

To complete the preceding answers (the obvious remaining part). If ${S\subset\mathbb R}$ is well ordered, then it is countable: indeed it has countable cofinality. Thus well-ordered subsets of R are exactly countable ordinals.

To complete the picture (the obvious remaining part). If ${S\subset\mathbb R}$ is well ordered, then it is countable: indeed it has countable cofinality. Thus well-ordered subsets of R are exactly countable ordinals.

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Pietro Majer
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To complete Robin Chapman's answerthe preceding answers (the obvious remaining part): if. If ${S\subset\mathbb R}$ is well ordered, then it is countable: indeed it has countable cofinality. Thus well-ordered subsets of R are exactly countable ordinals.

To complete Robin Chapman's answer (the obvious remaining part): if ${S\subset\mathbb R}$ is well ordered, then it is countable: indeed it has countable cofinality. Thus well-ordered subsets of R are exactly countable ordinals.

To complete the preceding answers (the obvious remaining part). If ${S\subset\mathbb R}$ is well ordered, then it is countable: indeed it has countable cofinality. Thus well-ordered subsets of R are exactly countable ordinals.

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Pietro Majer
  • 60.5k
  • 4
  • 122
  • 269

To complete Robin Chapman's answer (the obvious remaining part): if ${S\subset\mathbb R}$ is well ordered, then it is countable: indeed it has countable cofinality. Thus well-ordered subsets of R are exactly countable ordinals.