# Holomorphic form

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of degree on a complex manifold A differential form of type that satisfies the condition , i.e. a form that can be written in the local coordinates on as where are holomorphic functions (cf. Holomorphic function). The holomorphic forms of degree form a vector space over the field ; is the space of holomorphic functions on .

On a compact Kähler manifold the space coincides with the space of harmonic forms of type (cf. Harmonic form), hence is the first Betti number of . Holomorphic forms on a Riemann surface are also known as differentials of the first kind; if is compact, is equal to its genus (cf. Genus of a curve).

The spaces , , form a locally exact complex with respect to the operator , known as the holomorphic de Rham complex. If is a Stein manifold, then the cohomology spaces of this complex are isomorphic to the complex cohomology spaces , and if .

Holomorphic forms with values in some analytic vector bundle (cf. Vector bundle, analytic) over are defined in the same manner (here, holomorphic -forms are holomorphic sections of the bundle). The germs of holomorphic forms of degree with values in form a locally free analytic sheaf . The Dolbeault complex of forms of type , , with values in is a fine resolution of this sheaf, so that (the Dolbeault–Serre theorem , ).

The definition of holomorphic forms can be extended to complex-analytic spaces. It is sufficient to do this for local models, i.e. for the case of a space that is an analytic subspace of a domain . The sheaf of germs of holomorphic -forms in is defined as where is the sheaf of germs of holomorphic -forms in , while consists of the germs of forms of the type  where is the sheaf of ideals which define . The holomorphic de Rham complex of is also defined, but it is not locally exact. For this complex to be locally exact at a point starting from the -th degree it is sufficient that has, in a neighbourhood of , a holomorphic contraction onto a local analytic set for which .

How to Cite This Entry:
Holomorphic form. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Holomorphic_form&oldid=15455
This article was adapted from an original article by A.L. Onishchik (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article