# Structures on manifolds

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There are three main types of structures important on manifolds. The foundational geometric structures are piecewise linear, mostly studied in geometric topology, and smooth manifold structures on a given topological manifold, which are the concern of differential topology as far as classification goes. Building on a smooth structure, there are:

- various G-structures, which relate the tangent bundle to some subgroup
*G*of the general linear group - structures defined by holonomy conditions.

These can be related, and (for example for Calabi–Yau manifolds) their existence can be predicted using discrete invariants.