The differential forms on decompose into forms of type , sometimes called -forms. For example, on , the exterior algebra decomposes into four types:
(1)
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(2)
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where , , and denotes the direct sum. In general, a -form is the sum of terms with s and s. A -form decomposes into a sum of -forms, where .
For example, the 2-forms on decompose as
(3)
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(4)
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The decomposition into forms of type is preserved by holomorphic functions. More precisely, when is holomorphic and is a -form on , then the pullback is a -form on .
Recall that the exterior algebra is generated by the one-forms, by wedge product and addition. Then the forms of type are generated by
(5)
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The subspace of the complex one-forms can be identified as the -eigenspace of the almost complex structure , which satisfies . Similarly, the -eigenspace is the subspace . In fact, the decomposition of determines the almost complex structure on .
More abstractly, the forms into type are a group representation of , where acts by multiplication by .