Delta-ring

（重定向自Delta ring）

In mathematics, a nonempty collection of sets $\mathcal{R}$ is called a δ-ring (pronounced delta-ring) if it is closed under union, relative complementation, and countable intersection:

If only the first two properties are satisfied, then $\mathcal{R}$ is a ring but not a δ-ring. Every σ-ring is a δ-ring, but not every δ-ring is a σ-ring.

单词	Delta ring
释义	Delta ring 英语百科 Delta-ring （重定向自Delta ring） In mathematics, a nonempty collection of sets $\mathcal{R}$ is called a δ-ring (pronounced delta-ring) if it is closed under union, relative complementation, and countable intersection: If only the first two properties are satisfied, then $\mathcal{R}$ is a ring but not a δ-ring. Every σ-ring is a δ-ring, but not every δ-ring is a σ-ring.
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