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In mathematics, antiholomorphic functions (also called antianalytic functions) are a family of functions closely related to but distinct from holomorphic functions.

A function of the complex variable z defined on an open set in the complex plane is said to be antiholomorphic if its derivative with respect to z exists in the neighbourhood of each and every point in that set, where z is the complex conjugate.

There is an entry about the concept of an anti-holomorphic function in the Encyclopedia of Mathematics.[1] According to this entry the term anti-analytic function refers to the same concept. Anti-holomorphic function and anti-analytic function are synonyms of each other. According to [1]

'[a] function $${\displaystyle f(z)=u+iv}$$ of one or more complex variables $${\displaystyle z=\left(z_{1},\dots {},z_{n}\right)\in {\bf {C}}^{n}}$$ [is said to be anti-holomorphic if is the complex conjugate of a holomorphic function $${\displaystyle {\overline {f\left(z\right)}}=u-iv}'.$$

One can show that if f(z) is a holomorphic function on an open set D, then f(z) is an antiholomorphic function on D, where D is the reflection against the x-axis of D, or in other words, D is the set of complex conjugates of elements of D. Moreover, any antiholomorphic function can be obtained in this manner from a holomorphic function. This implies that a function is antiholomorphic if and only if it can be expanded in a power series in z in a neighborhood of each point in its domain. Also, a function f(z) is antiholomorphic on an open set D if and only if the function f(z) is holomorphic on D.

If a function is both holomorphic and antiholomorphic, then it is constant on any connected component of its domain.

Encyclopedia of Mathematics, Springer and The European Mathematical Society, https://encyclopediaofmath.org/wiki/Anti-holomorphic_function, As of 11 September 2020, This article was adapted from an original article by E. D. Solomentsev (originator), which appeared in Encyclopedia of Mathematics, ISBN 1402006098.