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Maths › 03. Logic and Foundations ›

4.4 Isomorphism

Structures are often presented using particular sets, symbols, and operations, but many mathematical questions concern the structure itself rather than the specific names of its elements. Isomorphism formalizes this idea by identifying structures that have the same internal organization, even when their underlying domains are different. Definition 4.31 (Isomorphism) Let $\mathcal A$ and $\mathcal B$ be structures for the same signature. An isomorphism from $\mathcal A$ to $\mathcal B$ is...
logic model theory isomorphism invariants May 2, 2026
Maths › 00. General Mathematics ›

04.4 Invariants

4.4 Invariants and Classification An invariant is a property, quantity, or structure that remains unchanged under a chosen class of transformations. Invariants are central to structural thinking. They allow us to compare objects without depending on representation. If two objects are isomorphic, their structural invariants agree. Therefore, if an invariant differs, the objects cannot be isomorphic. For example, two finite sets with different cardinalities cannot be bijective. Two vector spaces...
mathematics structure invariants classification isomorphism May 2, 2026
Maths › 00. General Mathematics ›

04. Structural Thinking

Chapter 4. Structural Thinking Mathematics becomes powerful when it shifts from individual objects to structures. Instead of studying each example in isolation, structural thinking identifies patterns that apply across many instances. This chapter gives an overview of that approach. A structure consists of objects together with operations, relations, and laws. Groups, vector spaces, graphs, and topological spaces are all examples. Once a structure is defined, attention moves from the objects...
mathematics structure abstraction invariants May 2, 2026