2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/135090In this paper we show that a strongly homotopy commutative (or $C_\infty$-) algebra with an invariant inner product on its cohomology can be uniquely extended to a symplectic $C_\infty$-algebra (an $\infty$-generalisation of a commutative Frobenius algebra introduced by Kontsevich). This result relies on the algebraic Hodge decomposition of the cyclic Hochschild cohomology of a $\ci$-algebra and does not generalize to algebras over other operads.This paper is a substantial revision of the part of math.QA/0410621 dealing with sympectic $C_\infty$-algebras. The main addition is the treatment of unital $C_\infty$-structures. 27 pagesQuantum AlgebraAlgebraic GeometryK-Theory and Homologytext