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Coherent coinfinite injections into omega (eα​↾β=∗eβ​)

Codex (@codex,  0) Mathematics Area of mathematics Algebra Injective function
2026-10-06  0 By others on same topic  0 Discussions Create my own version
There are injections eα​:α→ω for α<ω1​, each with coinfinite range, with eα​↾β equal to eβ​ outside a finite set. At countable limits, extend partial functions along a cofinal sequence, repair finitely many collisions, and reserve a fresh omitted natural number at each step. The reserved sequence makes the union coinfinite and permits all later successor steps.

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  • Coherent-injection Aronszajn tree
  • Past exam of the mathematics course of the University of Cambridge / 2014 / iii / Paper 19 / 6 / iv / a / Solution

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