CorollaryStatement: AI-adaptedProof: AI-adaptedSession-authored (Fable 5 assisted)precheck passjudge pass (deepseek-v4-pro + gpt-5.6-terra)audited 2026-08-21

How statement and proof provenance work

The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.

Literature-sourced: the exact statement appears in a cited source; only wording and notation differ.
AI-adapted: a semantically identical restatement of literature-sourced material, modulo indexing, notation, and boundary cases adopted by the library.
AI-generated: a genuinely novel statement formulated by AI, with no source for the claim itself.

These labels describe origin, not correctness: citations and verification chips remain separate evidence.

Holomorphic functions are real analytic and smooth in their two real coordinates

Statement

Let $U \subseteq C$ be open and let $f = u + i v : U \to C$ be holomorphic. Under the coordinate identification $C = R^{2}$ , the map $(u, v) : U \to R^{2}$ is real analytic in the sense of Real-analytic maps between open subsets of the coordinate plane and is of class $C^{k}$ for every natural $k$ , hence smooth.

Facts & Assumptions

Given: The identification of the complex plane with the real coordinate plane from $C$ is the real coordinate plane, with coordinate arithmetic, an open set $U$ , and a holomorphic function $f = u + i v$ on $U$ .

[L1]

Every holomorphic function equals its Taylor series throughout the largest centred open disc contained in its domain (A holomorphic function equals its Taylor series throughout the largest centred disc in its domain).

[L2]

For complex $z, w$ and a natural $n$ , $(z + w)^{n} = \sum_{p \leq n} (\binom{n}{p}) z^{p} w^{n - p}$ , with each binomial coefficient regarded as a complex scalar (The binomial theorem over the complex field).

[L3]

A smooth planar map is real analytic when each component equals its total-degree Taylor series on a neighbourhood of every point (Real-analytic maps between open subsets of the coordinate plane).

[L4]

A holomorphic function has complex derivatives of every natural order locally (All higher complex derivatives exist and satisfy Cauchy's integral formula on an interior circle).

[L5]

If $f = u + i v$ is complex differentiable, then $f^{'} = u_{x} + i v_{x} = v_{y} - i u_{y}$ and the Cauchy–Riemann equations hold (Complex differentiability is equivalent to real total differentiability together with a complex-linear derivative, with $\partial_{\overset{ˉ}{z}} f = 0$ , or with the Cauchy–Riemann equations).

[L6]

A real function is $C^{k}$ when every coordinate-derivative word of length at most $k$ , including the word of length zero, exists and is continuous ( $C^{k}$ maps and multi-index derivative notation in Euclidean space).

[L7]

Every complex power series converges absolutely and uniformly on closed subdiscs strictly inside its disc of convergence (A complex power series converges absolutely and uniformly on every closed subdisc strictly inside its disc of convergence).

[L8]

A complex differentiable function is continuous (Complex differentiability at a point implies continuity there).

[L9]

If $p \leq n$ , then the complex scalar corresponding to $(\binom{n}{p})$ is $n! / (p! (n - p)!)$ ( $(\binom{n}{k}) k! (n - k)! = n!$ for $k \leq n$ ; hence $(\binom{n}{k}) k! = n^{\underline{k}}$ , the quotient $n! / (k! (n - k)!)$ is a natural number, and $(\binom{n}{k}) = (\binom{n}{n - k})$ ).

Proof

technique · direct

1.1

Fix $a \in U$ . By [L1], there is $R > 0$ such that $f (a + h) = \sum_{n \geq 0} c_{n} h^{n}$ for $∣ h ∣ < R$ , where $c_{n} = f^{(n)} (a) / n!$ .

2.1

Write $h = x + i y$ . By [L2], $h^{n} = \sum_{p \leq n} (\binom{n}{p}) x^{p} (i y)^{n - p}$ ; if $∣ x ∣ + ∣ y ∣ < R$ , [L7] and the binomial identity give absolute convergence of the resulting total-degree series because the sum of the absolute values in degree $n$ is $∣ c_{n} ∣ (∣ x ∣ + ∣ y ∣)^{n}$ .

step 1.1L2L7algebra

3.1

From [L5], $\partial_{x} f = f^{'}$ and $\partial_{y} f = i f^{'}$ ; induction using [L4] therefore gives $\partial_{x}^{p} \partial_{y}^{q} f (a) = i^{q} f^{(p + q)} (a)$ . Taking $n = p + q$ in step 2.1 and using [L9], the coefficient of $x^{p} y^{q}$ is $c_{p + q} (\binom{p + q}{p}) i^{q} = D^{(p, q)} f (a) / (p! q!)$ .

step 1.1step 2.1L4L5L9algebra

4.1

Taking real and imaginary parts in the absolutely convergent expansion of step 2.1, and using the coefficient identification of step 3.1, gives the total-degree Taylor series of $u$ and $v$ on $∣ x ∣ + ∣ y ∣ < R$ .

step 2.1step 3.1

5.1

More generally, every coordinate-derivative word with $p$ occurrences of $x$ and $q$ occurrences of $y$ is the corresponding real or imaginary component of $i^{q} f^{(p + q)}$ ; [L4] makes the next complex derivative exist, [L8] makes every $f^{(p + q)}$ continuous, and the word of length zero is $f$ itself, so [L6] makes both components $C^{k}$ for every natural $k$ . Thus the map is smooth, and step 4.1 now satisfies the opening hypothesis of [L3], proving real analyticity as well.

step 3.1step 4.1L3L4L5L6L8∎

Depends on

Used by

Nothing in the library uses this result yet.

Dependency tree · two levels

62 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.

Sources

Michael Taylor, Introduction to Analysis in Several Variables, Ch. 2 §2.2, Exercise 4 (standard reference, not scraped)
Lars Ahlfors, Complex Analysis, 3rd ed., Ch. 5 §1.2 (standard reference, not scraped)
E. Stein and R. Shakarchi, Complex Analysis, Ch. 2 §4 (standard reference, not scraped)