It may belong to the geometric topology category of O 18. The following website contains all the classification numbers. You can check it again. Here are the classification numbers I know:
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O 1-0 mathematical theory
O 1-6 math reference books
O 1-8 calculation tool
O 1 1 classical mathematics
O 1 19 China mathematics
O 12 elementary mathematics
O 13 advanced mathematics
O 14 Mathematical Logic and Mathematical Basis
O 15 algebra, number theory, combinatorial theory
O 17 mathematical analysis
O 18 geometry and topology
O 19 power system theory
O2 1 Probability Theory and Mathematical Statistics
Research on O22 Operation
O23 Cybernetics and Information Theory (Mathematical Theory)
O24 computational mathematics
O29 applied mathematics
O 1-64 mathematical table
O 1-64 1 multiplication table, factor table and prime number table.
O 1-642 reciprocal table
O 1-643 power supply and square table
O 1-644 logarithmic table
O 1-645 trigonometric function table
O 1-646 integral table
O 1-647 tables for probability theory and mathematical statistics
O 1-648 special menu
O 1-649 calculation mathematical table
O 1 12 China classical mathematics
O113/117 classical mathematics in various countries
O 12 1 arithmetic
O 122 elementary algebra
O 123 elementary geometry
O 124 triangle
O 122. 1 algebraic expression
Equation O 122.2
O 122.3 inequality
O 122.4 permutation, combination and binomial theorem
O 122.5 maximum and minimum values
O 122.6 Logarithmic sum index
O 122.7 series
O 123 438+0 plane geometry
O 123.2 solid geometry
O 123.3 geometric theory
O 123.4 maximum and minimum values
O 123.5 trajectory and geometry
O 123.6 geometry of triangles and circles, modern geometry
O 124. 1 plane triangle
O 124.2 spherical triangle
O 14 1 mathematical logic (symbolic logic)
O 142 applied mathematical logic
O 143 mathematical basis
O 144 set theory
O 14 1. 1 propositional calculus, predicate calculus and class calculus.
O 14 1.2 proof theory
O 14 1.3 recursive theory (recursive function, feasibility theory)
O 14 1.4 model theory
O 14 1. 12 predicate calculus (propositional function calculus)
O 14 1. 13 calculus.
O 14 1.45438+0 nonstandard analysis
O 144. 1 basic concepts
O 144.2 paradox
O 144.3 axiomatic set theory
O 144.4 type theory
O 144.5 descriptive set theory (analytical set theory)
O 15 1 algebraic equation theory, linear algebra
O 152 group theory
O 153 abstract algebra (modern algebra)
O 154 Category Theory and Homology Algebra
O 155 differential algebra, differential algebra
O 156 number theory
O 157 combinatorial mathematics (combinatorics)
O 158 discrete mathematics
O 159 fuzzy mathematics
O 15 1. 1 algebraic equation theory
O 15 1.2 linear algebra
O 152 438+0 finite group theory
O 152.2 Abel group theory
O 152.3 linear group theory
O 152.4 topological group theory
O 152.5 lie groups
O 152.6 group representation theory
Generalization of O 152.7 group
Application of O 152.8 Group Theory
O 153 438+0 poset and lattice theory
O 153.2 boolean algebra
O 153.3 ring theory
O 153.4 domain theory
O 153.5 universal algebra
O 154 438+0 category theory
O 154.2 homology algebra
O 154.3 algebraic k theory
O 156.6438+0 elementary number theory
O 156.2 algebraic number theory
O 156.3 geometric number theory
O 156.4 analytic number theory
O 156.5 quadratic form (quadratic homogeneous form)
O 156.6 transcendental number theory
O 156.7 Diophantine analysis (Diophantine number theory)
O 157. 1 combination analysis
O 157.2 combination design
O 157.3 combinatorial geometry
O 157.4 coding theory (algebraic coding theory)
O 157.5 graph theory
Application of Graph Theory in O 157.6
O 17 1 analysis basis
O 172 calculus
O 173 infinite series theory (series theory)
O 174 function theory
O 175 differential equation and integral equation
O 176 variational method
Functional analysis of O 177
O 178 inequality and others
O 172 438+0 calculus
O 172.2 integral calculus
O 174. 1 real analysis, real variable function
O 174.2 Fourier analysis (classical harmonic analysis)
O 174.3 Harmonic Function and Potential Theory
O 174.4 function construction theory
O 174.5 complex analysis and complex variable function
O 174.6 special functions
O 174 438+0 Bessel function
O 174.62 spherical harmonic function
O 174.63 cylindrical harmonic function
O 174.64 elliptic harmonic function
O 174.66 Euler integral
Geometric theory of O 174 438+0 simple complex variable function
O 174.52 whole function theory and meromorphic function theory (semi-meromorphic function theory)
O 174.53 Algebraic Function Theory
O 174.54 elliptic function, abelian function, automorphic function
O 174.55 Quasi-conformal mapping (quasi-conformal transformation), quasi-analytic function, generalized analytic function.
O 174.56 multi-complex variable function
O 174 438+0 approximation theory
O 174.42 interpolation theory
O 174.43 torque problem
O 174 438+0 orthogonal series (Fourier series)
O 174.22 Fourier integral (Fourier transform)
O 174.23 almost periodic function
O 174. 1 1 description theory
O 174. 12 measurement theory
O 174. 13 convex function and convex set theory
O 174. 14 polynomial theory
O 175. 1 ordinary differential equation
O 175.2 partial differential equation
O 175.3 differential operator theory
O 175.4 higher order partial differential equations (group)
O 175.5 integral equation
O 175.6 integro-differential equation
O 175.7 difference differential equation
O 175.8 boundary value problem
O 175.9 eigenvalue and eigenvalue function problems
O 175. 1 1 analytic theory
O 175 438+02 qualitative theory
O 175 438+03 stability theory
O 175. 14 nonlinear ordinary differential equation
O 175.5438+05 Ordinary differential equation in abstract space
O 175+0 stability theory
O 175.22 first-order partial differential equation
O 175.23 second-order partial differential equation
O 175.24 mathematical equation
O 175.25 elliptic equation
O 175.26 parabolic equation
O 175.27 hyperbolic equation
O 175.28 mixed equation
O 175.29 nonlinear partial differential equation
O 176. 1 minimum surface equation
O 176.2 isoperimetric problem
O 176.3 large-scale variational method
O 177 438+0 Hilbert space and its linear operator theory
O 177.2 Banach space and its linear operator theory
O 177.3 linear space theory (vector space)
O 177.4 generalized function theory
O 177.5 Banach algebra (normed algebra), topological algebra, abstract harmonic analysis
O 177.6 integral transformation and operator calculus
O 177.7 spectral theory
O 177.8 integration theory (based on functional analysis)
Nonlinear functional analysis of O 177 438+0
Application of O 177.92 functional analysis
O 177.99 others
O 18 1 geometric basis (geometric principle)
O 182 analytic geometry
O 183 vector and tensor analysis
O 184 Non-Euclidean Geometry and Multidimensional Space Geometry
O 185 projective geometry and descriptive geometry
O 186 differential geometry, integral geometry
O 187 algebraic geometry
O 189 topology (situational geometry)
Vector analysis of V o 183 438+0
Tensor analysis of O 183.2
O 192 global analysis, manifold analysis, catastrophe theory
O 193 differential power system
O22 1 programming theory (mathematical programming)
O223 overall planning method
Mathematical Theory of O224 Optimization
O225 game theory (game theory)
O226 Queuing Theory (Stochastic Service System)
O227 inventory theory
O228 renewal theory
O229 search theory
Numerical analysis of v 024 1
Mathematical Simulation and Approximate Calculation of O242
O243 graphic mathematics, graphic mathematics
[O244] programming
O245 numerical software
O246 numerical parallel calculation
O24 1. 1 error theory
{O24 1.2} least square method
O24 1.3 interpolation method
O24 1.4 numerical integration method and numerical differentiation method
O24 1.5 numerical approximation
Calculation method of O24 1.6 linear algebra
Numerical solutions of O24 1.7 nonlinear algebraic equations and transcendental equations
Numerical solutions of O24 1.8 differential equation and integral equation
O242. 1 Mathematical Simulation
O242.2 approximate calculation