Difference between revisions of "Diamond principle"
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Diamond principle $♢$ (TeX \diamondsuit) is the statement what?...
Variants:
 $♢_κ$ or $♢(κ)$ is the statement “There exist sets $(S_αα < κ)$, $S_α ⊆ α$ ($α < κ$) such that for any $X ∈ κ$ the set $\{αX ∩ α = S_α\}$ is Mahlo” introduced in [1].[2]
Results:
 If $κ$ is ethereal and $2^\underset{\smile}{κ} = κ$, then $♢_κ$ holds (where $2^\underset{\smile}{κ} = \bigcup \{ 2^α  α < κ \}$ is the weak power of $κ$).[2]
 If $κ$ is ineffable, weakly ineffable or subtle, then $♢_κ$ holds.[1][2]
References
 Jensen, Ronald and Kunen, Kenneth. Some combinatorial properties of $L$ and $V$. Unpublished, 1969. www bibtex
 Ketonen, Jussi. Some combinatorial principles. Trans Amer Math Soc 188:387394, 1974. DOI bibtex
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