Map of Mathematics

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Map of Mathematics

A comprehensive overview of mathematical fields, their connections, and foundational structures.

1. Foundations of Mathematics

At the deepest level, mathematics rests on questions about its own nature and structure.

1.1 Logic

• Propositional Logic: Studies logical connectives $\land$ (and), $\lor$ (or), $

eg$ (not), $\rightarrow$ (implies)

• Predicate Logic: Introduces quantifiers $\forall$ (for all) and $\exists$ (there exists)
• Key Result: Gödel's Incompleteness Theorems
• First: Any consistent formal system $F$ capable of expressing arithmetic contains statements that are true but unprovable in $F$
• Second: Such a system cannot prove its own consistency

1.2 Set Theory

• Zermelo-Fraenkel Axioms with Choice (ZFC): The standard foundation
• Key Concepts:
• Empty set: $\emptyset$
• Union: $A \cup B = \{x : x \in A \text{ or } x \in B\}$
• Intersection: $A \cap B = \{x : x \in A \text{ and } x \in B\}$
• Power set: $\mathcal{P}(A) = \{B : B \subseteq A\}$
• Cardinality: $|A|$, with $|\mathbb{N}| = \aleph_0$ (countable infinity)
• Continuum Hypothesis: Is there a set with cardinality strictly between $|\mathbb{N}|$ and $|\mathbb{R}|$?

1.3 Category Theory

• Objects and Morphisms: Abstract structures and structure-preserving maps
• Key Concepts:
• Functors: $F: \mathcal{C} \to \mathcal{D}$ (maps between categories)
• Natural transformations: $\eta: F \Rightarrow G$
• Universal properties and limits
• Philosophy: "It's all about the arrows" — relationships matter more than objects

1.4 Type Theory

• Dependent Types: Types that depend on values
• Curry-Howard Correspondence:

• Applications: Proof assistants (Coq, Lean, Agda)

2. Algebra

The study of structure, operations, and their properties.

2.1 Linear Algebra

• Vector Spaces: A set $V$ over field $F$ with addition and scalar multiplication
• Key Structures:
• Linear transformation: $T: V \to W$ where $T(\alpha u + \beta v) = \alpha T(u) + \beta T(v)$
• Matrix representation: $[T]_{\mathcal{B}}$
• Eigenvalue equation: $Av = \lambda v$
• Fundamental Theorem: Every matrix $A$ has a Jordan normal form
• Singular Value Decomposition:

2.2 Group Theory

• Definition: A group $(G, \cdot)$ satisfies:
• Closure: $a, b \in G \Rightarrow a \cdot b \in G$
• Associativity: $(a \cdot b) \cdot c = a \cdot (b \cdot c)$
• Identity: $\exists e \in G$ such that $e \cdot a = a \cdot e = a$
• Inverses: $\forall a \in G, \exists a^{-1}$ such that $a \cdot a^{-1} = e$
• Key Examples:
• Symmetric group $S_n$ (all permutations of $n$ elements)
• Cyclic group $\mathbb{Z}/n\mathbb{Z}$
• General linear group $GL_n(\mathbb{R})$ (invertible $n \times n$ matrices)
• Lagrange's Theorem: If $H \leq G$, then $|H|$ divides $|G|$
• Classification of Finite Simple Groups: Completed in 2004 (~10,000 pages)

2.3 Ring Theory

• Definition: A ring $(R, +, \cdot)$ has:
• $(R, +)$ is an abelian group
• Multiplication is associative
• Distributivity: $a(b + c) = ab + ac$
• Key Examples:
• Integers $\mathbb{Z}$
• Polynomials $R[x]$
• Matrices $M_n(R)$
• Ideals: $I \subseteq R$ is an ideal if $RI \subseteq I$ and $IR \subseteq I$
• Quotient Rings: $R/I$

2.4 Field Theory

• Definition: A field is a commutative ring where every nonzero element has a multiplicative inverse
• Examples: $\mathbb{Q}$, $\mathbb{R}$, $\mathbb{C}$, $\mathbb{F}_p$ (finite fields)
• Field Extensions: $L/K$ where $K \subseteq L$
• Galois Theory: Studies field extensions via their automorphism groups
• Fundamental Theorem: There is a correspondence between intermediate fields of $L/K$ and subgroups of $\text{Gal}(L/K)$

2.5 Representation Theory

• Definition: A representation of group $G$ is a homomorphism $\rho: G \to GL(V)$
• Characters: $\chi_\rho(g) = \text{Tr}(\rho(g))$
• Key Result: Characters of irreducible representations form an orthonormal basis

3. Analysis

The rigorous study of continuous change, limits, and infinity.

3.1 Real Analysis

• Limits: $\lim_{x \to a} f(x) = L$ iff $\forall \varepsilon > 0, \exists \delta > 0$ such that $0 < |x - a| < \delta \Rightarrow |f(x) - L| < \varepsilon$
• Continuity: $f$ is continuous at $a$ if $\lim_{x \to a} f(x) = f(a)$
• Differentiation:

• Integration (Riemann):

• Fundamental Theorem of Calculus:

3.2 Measure Theory

• $\sigma$-Algebra: Collection of sets closed under complements and countable unions
• Measure: $\mu: \Sigma \to [0, \infty]$ with:
• $\mu(\emptyset) = 0$
• Countable additivity: $\mu\left(\bigcup_{i=1}^\infty A_i\right) = \sum_{i=1}^\infty \mu(A_i)$ for disjoint $A_i$
• Lebesgue Integral:

3.3 Complex Analysis

• Holomorphic Functions: $f: \mathbb{C} \to \mathbb{C}$ is holomorphic if $f'(z)$ exists
• Cauchy-Riemann Equations: If $f = u + iv$, then

• Cauchy's Integral Formula:

• Residue Theorem:

3.4 Functional Analysis

• Banach Spaces: Complete normed vector spaces
• Hilbert Spaces: Complete inner product spaces
• Inner product: $\langle \cdot, \cdot \rangle: V \times V \to \mathbb{C}$
• Norm: $\|v\| = \sqrt{\langle v, v \rangle}$
• Key Theorems:
• Hahn-Banach (extension of linear functionals)
• Open Mapping Theorem
• Closed Graph Theorem
• Spectral Theorem: Normal operators on Hilbert spaces have spectral decompositions

3.5 Differential Equations

• Ordinary Differential Equations (ODEs):
• First order: $\frac{dy}{dx} = f(x, y)$
• Linear: $y^{(n)} + a_{n-1}y^{(n-1)} + \cdots + a_0 y = g(x)$
• Partial Differential Equations (PDEs):
• Heat equation: $\frac{\partial u}{\partial t} = \alpha

abla^2 u$

• Wave equation: $\frac{\partial^2 u}{\partial t^2} = c^2

abla^2 u$

• Laplace equation: $

abla^2 u = 0$

• Schrödinger equation: $i\hbar \frac{\partial \psi}{\partial t} = \hat{H}\psi$

4. Geometry and Topology

The study of space, shape, and structure.

4.1 Euclidean Geometry

• Euclid's Postulates: Five axioms defining flat space
• Key Results:
• Pythagorean theorem: $a^2 + b^2 = c^2$
• Sum of angles in triangle: $180°$
• Parallel postulate: Given a line and a point not on it, exactly one parallel exists

4.2 Non-Euclidean Geometries

• Hyperbolic Geometry (negative curvature):
• Multiple parallels through a point
• Sum of angles in triangle: $< 180°$
• Model: Poincaré disk with metric $ds^2 = \frac{4(dx^2 + dy^2)}{(1 - x^2 - y^2)^2}$
• Elliptic/Spherical Geometry (positive curvature):
• No parallels
• Sum of angles in triangle: $> 180°$

4.3 Differential Geometry

• Manifolds: Spaces locally homeomorphic to $\mathbb{R}^n$
• Tangent Spaces: $T_p M$ at each point $p$
• Riemannian Metric: $g_{ij}$ defining distances and angles

• Curvature:
• Gaussian curvature: $K = \kappa_1 \kappa_2$ (product of principal curvatures)
• Riemann curvature tensor: $R^i_{\ jkl}$
• Ricci curvature: $R_{ij} = R^k_{\ ikj}$
• Scalar curvature: $R = g^{ij} R_{ij}$
• Gauss-Bonnet Theorem:

where $\chi(M)$ is the Euler characteristic

4.4 Topology

• Topological Space: $(X, \tau)$ where $\tau$ is a collection of "open sets"
• Homeomorphism: Continuous bijection with continuous inverse
• Key Invariants:
• Connectedness
• Compactness
• Euler characteristic: $\chi = V - E + F$

4.5 Algebraic Topology

• Fundamental Group: $\pi_1(X, x_0)$ — loops up to homotopy
• $\pi_1(S^1) = \mathbb{Z}$
• $\pi_1(\mathbb{R}^n) = 0$
• Higher Homotopy Groups: $\pi_n(X)$
• Homology Groups: $H_n(X)$ — "holes" in dimension $n$
• $H_0$ counts connected components
• $H_1$ counts 1-dimensional holes (loops)
• $H_2$ counts 2-dimensional holes (voids)
• Cohomology: Dual theory with cup product structure

4.6 Algebraic Geometry

• Affine Variety: Zero set of polynomials

• Projective Variety: Variety in projective space $\mathbb{P}^n$
• Schemes: Generalization using commutative algebra
• Sheaves: Local-to-global data structures
• Key Results:
• Bézout's Theorem: Degree $m$ and $n$ curves intersect in $mn$ points (counting multiplicities)
• Riemann-Roch Theorem (for curves):

5. Number Theory

The study of integers and their generalizations.

5.1 Elementary Number Theory

• Divisibility: $a | b$ iff $\exists k$ such that $b = ka$
• Prime Numbers: $p > 1$ with only divisors $1$ and $p$
• Fundamental Theorem of Arithmetic: Every integer $> 1$ factors uniquely into primes

• Modular Arithmetic: $a \equiv b \pmod{n}$ iff $n | (a - b)$
• Euler's Theorem: If $\gcd(a, n) = 1$, then $a^{\phi(n)} \equiv 1 \pmod{n}$
• Fermat's Little Theorem: If $p$ is prime and $p

mid a$, then $a^{p-1} \equiv 1 \pmod{p}$

5.2 Analytic Number Theory

• Prime Number Theorem:

where $\pi(x)$ counts primes $\leq x$

• Riemann Zeta Function:

• Riemann Hypothesis: All non-trivial zeros of $\zeta(s)$ have real part $\frac{1}{2}$
• Dirichlet L-Functions: Generalization for arithmetic progressions

5.3 Algebraic Number Theory

• Number Fields: Finite extensions of $\mathbb{Q}$
• Ring of Integers: $\mathcal{O}_K$ — algebraic integers in $K$
• Unique Factorization Failure: $\mathcal{O}_K$ may not be a UFD
• Example: In $\mathbb{Z}[\sqrt{-5}]$: $6 = 2 \cdot 3 = (1 + \sqrt{-5})(1 - \sqrt{-5})$
• Ideal Class Group: Measures failure of unique factorization
• Class Number Formula:

5.4 Famous Conjectures and Theorems

• Fermat's Last Theorem (proved by Wiles, 1995):

• Goldbach's Conjecture (open): Every even integer $> 2$ is the sum of two primes
• Twin Prime Conjecture (open): Infinitely many primes $p$ where $p + 2$ is also prime
• ABC Conjecture: For coprime $a + b = c$, $\text{rad}(abc)^{1+\varepsilon} > c$ for almost all triples

6. Combinatorics

The study of discrete structures and counting.

6.1 Enumerative Combinatorics

• Counting Principles:
• Permutations: $P(n, k) = \frac{n!}{(n-k)!}$
• Combinations: $\binom{n}{k} = \frac{n!}{k!(n-k)!}$
• Binomial Theorem:

• Generating Functions:
• Ordinary: $F(x) = \sum_{n=0}^{\infty} a_n x^n$
• Exponential: $F(x) = \sum_{n=0}^{\infty} a_n \frac{x^n}{n!}$

6.2 Graph Theory

• Definitions:
• Graph $G = (V, E)$: vertices and edges
• Degree: $\deg(v) = |\{e \in E : v \in e\}|$
• Handshaking Lemma: $\sum_{v \in V} \deg(v) = 2|E|$
• Euler's Formula (planar graphs): $V - E + F = 2$
• Key Problems:
• Graph coloring: $\chi(G)$ = chromatic number
• Four Color Theorem: Every planar graph is 4-colorable
• Hamiltonian cycles

6.3 Ramsey Theory

• Principle: "Complete disorder is impossible"
• Ramsey Numbers: $R(m, n)$ = minimum $N$ such that any 2-coloring of $K_N$ contains monochromatic $K_m$ or $K_n$
• $R(3, 3) = 6$
• $R(4, 4) = 18$
• $43 \leq R(5, 5) \leq 48$ (exact value unknown)

7. Probability and Statistics

7.1 Probability Theory

• Kolmogorov Axioms:

1. $P(A) \geq 0$ 2. $P(\Omega) = 1$ 3. Countable additivity: $P\left(\bigcup_{i} A_i\right) = \sum_{i} P(A_i)$ for disjoint $A_i$

• Conditional Probability: $P(A|B) = \frac{P(A \cap B)}{P(B)}$
• Bayes' Theorem:

• Expectation: $E[X] = \int x \, dF(x)$
• Variance: $\text{Var}(X) = E[(X - E[X])^2] = E[X^2] - (E[X])^2$

7.2 Key Distributions

7.3 Limit Theorems

• Law of Large Numbers:

• Central Limit Theorem:

8. Applied Mathematics

8.1 Numerical Analysis

• Root Finding: Newton's method: $x_{n+1} = x_n - \frac{f(x_n)}{f'(x_n)}$
• Interpolation: Lagrange, splines
• Numerical Integration: Simpson's rule, Gaussian quadrature
• Linear Systems: LU decomposition, iterative methods

8.2 Optimization

• Unconstrained: Find $\min_x f(x)$
• Gradient descent: $x_{k+1} = x_k - \alpha

abla f(x_k)$

• Constrained: Lagrange multipliers