A boundary locally defined by real-analytic functions so that near every point the defining functions admit convergent power-series expansions and the boundary is locally the zero set of such analytic functions.

Principle

Real-analytic regularity imposes rigid extension properties beyond infinite differentiability: local power-series expansion controls unique continuation, enables analytic continuation methods, and constrains possible local geometry more strongly than C∞.

Demonstration

As a demonstration, a domain with a real-analytic defining function in R^n allows reflection arguments and analytic continuation for solutions of elliptic equations, often implying that boundary data which vanish to infinite order force vanishing in a neighborhood.

Misapplication

Assuming analytic properties from mere C∞ smoothness (for example expecting global analytic continuation or finite-degree determinacy) is a misapplication; C∞ data need not satisfy power-series convergence hypotheses.

Consequence

When valid, analytic boundary yields stronger rigidity: uniqueness of analytic continuation of harmonic or holomorphic objects, applicability of complex-analytic techniques in suitable settings, and sharp structure of singular expansions.

Reversal

The reversal is a boundary that is C∞ but not analytic, where infinite jets exist but do not arise from convergent power series, so analytic continuation and related rigidity phenomena fail.

Boundary

Scope covers boundaries that are real-analytic in local coordinates; it excludes merely smooth (C∞) boundaries that lack convergent series representations, and excludes complex-analytic structures unless the real-analytic setting is extended.

Semantic Tension

Tension appears between analytic and smooth categories: both admit derivatives of all orders, but analyticity's extra condition (convergent Taylor series) produces qualitatively different extension and uniqueness properties that are not captured by C∞ theory.

Synthesis

An analytic boundary is a strictly stronger regularity condition than smoothness: by requiring local convergent power-series descriptions, it yields rigidity and continuation properties that sharpen geometric and analytic control near the boundary.