9. Tutorial 5
The chapter explores key concepts related to cardinality and infinity in set theory, focusing on the relationships between different sets, their cardinalities, and properties of infinite sets. It discusses important theorems such as the Schroder-Bernstein theorem and offers proofs for various claims about countability and uncountability of sets. In addition, the chapter provides exercises and activities to reinforce the understanding of these concepts.
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Sections
Navigate through the learning materials and practice exercises.
What we have learnt
- Two sets can have the same cardinality if there exist injective mappings between them.
- There is no infinite set whose cardinality is strictly less than א₀, the cardinality of the set of positive integers.
- Any infinite set has a countably infinite subset.
Key Concepts
- -- Cardinality
- A measure of the 'number of elements' in a set, which can be finite or infinite.
- -- Injective Mapping
- A function where each element of the domain maps to a unique element in the codomain, ensuring no two elements in the domain map to the same element in the codomain.
- -- Countably Infinite
- A set is countably infinite if its elements can be listed in a sequence, meaning they can be put into one-to-one correspondence with the set of natural numbers.
- -- SchroderBernstein Theorem
- If there exist injective functions from set A to set B and from set B to set A, then the two sets have the same cardinality.
Additional Learning Materials
Supplementary resources to enhance your learning experience.