Gelfand Theory and Commutative C Star Algebras — Examples
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1 · Prerequisites
Abstract Algebra
- Binary Operations, Monoids, Groups and Subgroups
- Cosets, Index and Lagrange's Theorem
- Divisibility, Euclidean Domains, Principal Ideal Domains and Unique Factorisation
- Ideals, Quotient Rings and the Isomorphism Theorems for Rings
- Normal Subgroups and Quotient Groups
- Polynomial Rings, the Division Algorithm and Roots
- Rings, Subrings, Integral Domains and Fields
- Simple Field Extensions and the Construction of the Complex Numbers
Complex Analysis
- Analyticity of Holomorphic Functions; Liouville and Morera
- Complex Coordinate and Path Transport
- Complex Differentiability and the Cauchy–Riemann Equations
- Complex Power Series and Analytic Functions
- Contour Integration
- Goursat's Theorem and Cauchy's Theorem in a Convex Domain
- The Identity Theorem, the Maximum Principle and the Open Mapping Theorem
Functional Analysis
- Banach Alaoglu Goldstine and Krein Milman
- Banach Algebras Spectrum and Holomorphic Functional Calculus
- Banach Valued Integration and the Radon Nikodym Property
- Bounded Linear Operators and Quotient Spaces
- Complex Norms and Realification
- Complex Subspace Realification
- Dual Spaces Adjoint Operators and Annihilators
- Gelfand Theory and Commutative C Star Algebras
- Geometric Hahn Banach and Convex Separation
- Locally Convex Spaces and Continuous Separation
- Normed and Banach Spaces
- Orthonormal Bases, Parseval and Fourier Series
- The Analytic Hahn Banach Theorem
Linear Algebra
- Complexification, Realification and Real Structures
- Dual Spaces, Bilinear and Quadratic Forms, and Sylvester's Law of Inertia
- Linear Independence, Bases and Dimension
- Linear Transformations, Rank-Nullity and Quotient Spaces
- Matrices, the Matrix of a Linear Map, and Change of Basis
- Triangularisation, Generalised Eigenspaces and Jordan Canonical Form
- Vector Spaces, Linear Subspaces, Span and Direct Sums
Measure Theory
- Lebesgue Measure on Euclidean Space
- Measurable Functions and Simple Approximation
- Measures and Their Basic Properties
- Outer Measure and the Caratheodory Extension Theorem
- Pointwise Extended-Real Function Products
- Product Measures and the Fubini Tonelli Theorems
- Radon Measures and the Riesz Markov Kakutani Theorem
- Sigma Algebras and Borel Sets
- Signed and Complex Measures Hahn and Jordan
- The Lebesgue Integral and the Convergence Theorems
- The Lᵖ Spaces Holder Minkowski and Riesz Fischer
Real Analysis
- Absolute and Conditional Convergence; Rearrangement; Products
- Approximation and Compactness in C(K)
- Arc Length and Rectifiable Curves
- Areas of Elementary Plane Figures
- Bounded Variation and the Riemann–Stieltjes Integral
- Construction of the Real Numbers via Cauchy Sequences
- Construction of the Real Numbers via Dedekind Cuts
- Continuity, IVT, EVT, and Uniform Continuity
- Countability and Uncountability
- Foundations of the Real Numbers for Analysis
- Fundamental Trigonometric Identities
- Limits of Real Functions
- limsup, liminf, and Subsequential Limits
- Line Integrals and the Gradient Theorem
- Mixed Partials, Taylor Formulae, and Extrema
- Monotone Functions, Discontinuities, and Continuity Sets
- Monotone Sequences, Bolzano-Weierstrass, and Cauchy Completeness
- pi: the Equivalent Characterizations
- Power Series and Real-Analytic Functions
- Properties of the Integral and the Working FTC
- Rⁿ as a Normed Space; Vector-Valued Functions
- Roots, Rational Powers, and Classical Inequalities
- Sequences and Limits
- Sequences and Series of Functions; Uniform Convergence
- Series: Convergence and the Nonnegative Tests
- Sine, Cosine, and the Definition of Pi
- Suprema and Infima
- The Cantor Set, Baire Category, and Measure Zero in ℝ
- The Complex Exponential and Euler's Formula
- The Derivative and the Mean Value Theorems
- The Exponential Function
- The Fundamental Theorems of Calculus
- The Inverse and Implicit Function Theorems
- The Logarithm and General Powers
- The Riemann Integral in Rᵐ and Jordan Content
- The Riemann Integral: Definition and Integrability
- The Total Derivative in ℝᵐ → ℝⁿ
- Topology of ℝ
Set Theory
Topology
- Compactness
- Compactness in Metric Spaces
- Completeness, Completion, and Uniform Continuity
- Connectedness
- Convergence: Nets and Filters
- Countability Axioms and Cardinal Functions
- Function Space Topologies and the Exponential Law
- Hausdorff via the Diagonal
- Hereditary and Productive Behaviour of the Separation Axioms
- Metric Spaces
- Partitions of Unity and Paracompactness
- Separation Axioms: the Hierarchy
- Stone–Weierstrass in General
- Subspaces, Products, and Quotients
- The Topology of Euclidean Space
- The Tychonoff Embedding and the Stone–Čech Compactification
- Topological Spaces and Continuity
- Urysohn's Lemma and the Tietze Extension Theorem
2 · Logical flowchart
3 · Items
Example
Character space of C(K)
Example
Character space of the disc algebra
Example
Gelfand transform of ell one of Z
Counterexample
Gelfand transform of a Banach algebra need not be isometric
Example
Banach-Stone weighted composition isometries
Example
Free maximal ideals of C(N) and beta N
Example
Stone duality for a power set algebra
Example
Stone duality for a finite Boolean algebra
Example
C zero of a locally compact space
Example
Unitization corresponds to one point compactification
Remark
Wiener lemma is developed on the Fourier analysis track
Sources
- Vahid Shirbisheh, Lectures on C-star Algebras, v2 — Remark 3.1.36 and §3.1, printed pp. 54–67
- Theo Bühler and Dietmar A. Salamon, Functional Analysis — §5.5.1, printed pp. 258–267
- Theo Bühler and Dietmar A. Salamon, Functional Analysis — §5.5.1 and Chapter 4, printed pp. 258–267
- Vahid Shirbisheh, Lectures on C-star Algebras, v2 — §3.1, printed pp. 54–67
- Vahid Shirbisheh, Lectures on C-star Algebras, v2 — Definition 3.1.23 and §3.1, printed pp. 62–67
- Theo Bühler and Dietmar A. Salamon, Functional Analysis — Theorem 5.63 and §5.5.1, printed pp. 262–266
- Orr Shalit, Advanced Analysis Notes 14: the isometric structure of C(K) — Examples before Theorem 2, HTML lines 38–54
- L. Gillman, M. Henriksen and M. Jerison, On a Theorem of Gelfand and Kolmogoroff Concerning Maximal Ideals in Rings of Continuous Functions (1954) — §2, after Theorem 1, pp. 448–449. This endpoint was inaccessible in the current run; the exact local proof and failed recovery record are in the Batch 4 coverage ledger.
- Marcus Tressl, Stone Duality for Boolean Algebras — Example 2.3.2, p. 8; the beta-N universal-property verification is local from the declared Stone–Čech suppliers
- Marcus Tressl, Stone Duality for Boolean Algebras — Theorem 2.3.4, pp. 9–10, and Theorem 3.1.5, pp. 11–12; the finite computation is supplied locally
- Vahid Shirbisheh, Lectures on C-star Algebras, v2 — Example 3.1.39 and §3.1, printed pp. 54–67
- Dana P. Williams, Lecture Notes on the Spectral Theorem — §4, printed pp. 9–11
- Vahid Shirbisheh, Lectures on C-star Algebras, v2 — Proposition 3.1.16 and §3.1, printed pp. 60–61
- Vahid Shirbisheh, Lectures on C-star Algebras, v2 — §2.6 and §3.1, printed pp. 44–67