Diagonal Argument

Set Theory Jottings 22. Absoluteness March 11, 2026 - (0)
Prev TOC Next Let’s look again at the notion of definability, rewritten slightly: for any set A, x⊆A is definable over A if there is a first-order formula φ(y,ū) and elements ā∈A such that x={z∈A:φA(z,ā)} where φA is φ relativized to A, i.e., all quantifiers in φ range only over A. Very clearly the right-hand […]
Set Theory Jottings 21. The Constructible Universe March 5, 2026 - (0)
From Kepler to Ptolemy 23 January 20, 2026 - (0)
Set Theory Jottings 20. Consistency of GCH and AC: Overview December 27, 2025 - (0)
Set Theory Jottings 19. GCH implies AC. November 24, 2025 - (0)

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