A Betti number is the dimension of a real singular homology group; on a smooth manifold it is also the dimension of the corresponding de Rham cohomology group. For a finite-dimensional cohomology group on a closed Riemannian manifold, it equals the dimension of its space of harmonic representatives. Betti numbers can increase under a finite cover, so equality is a separate hypothesis, not a general covering-space theorem.
Articles by others on the same topic
In algebraic topology, Betti numbers are a sequence of integers that provide important information about the topology of a topological space. They are used to classify spaces based on their connectivity properties and to understand their shape and structure. Specifically, the \(n\)-th Betti number, denoted \(b_n\), represents the rank of the \(n\)-th homology group \(H_n(X)\) of a topological space \(X\).