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A capital H with a degree subscript and a space in brackets.
Also known as: Homology group, H n, Singular homology notation
Homology groups count holes of each dimension: H_0 counts connected pieces, H_1 counts loops, H_2 counts cavities. Unlike the fundamental group they are abelian and computable, which is why they are the workhorse invariant of algebraic topology.
Denotes the homology groups of a space, indexed by dimension.
Contexts: Mathematics
Counts holes by dimension, with the zeroth group recording connected components.
Contexts: Mathematics
Is abelian in every degree, which makes it computable where the fundamental group is not.
Contexts: Mathematics
A capital letter H with a small numeral below right, followed by a bracketed space name.