3. Countable and Uncountable Sets
The discussion focuses on the concepts of cardinality in sets, distinguishing between finite and infinite sets. The chapter categorizes infinite sets into countable and uncountable, explaining the definition of countable sets and providing examples and bijections for various sets. It concludes with the significance of understanding these classifications in mathematics.
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Sections
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What we have learnt
- The cardinality of a set is determined by the number of elements it contains.
- Countable sets can be finite or infinite, with infinite sets classified further into countably infinite and uncountable.
- A set is countably infinite if its cardinality is the same as the set of positive integers, denoted by aleph null (א0).
Key Concepts
- -- Cardinality
- A measure of the 'number of elements' in a set, denoted as |X| for a set X.
- -- Countable Sets
- Sets that have a cardinality that is either finite or matches that of the positive integers.
- -- Countably Infinite
- A specific type of infinite set that can be arranged in a sequence indexed by positive integers.
- -- Bijection
- A one-to-one correspondence between two sets, demonstrating they have the same cardinality.
- -- Aleph Null (א0)
- A notation representing the cardinality of any countably infinite set.
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