7
$\begingroup$

Let $\mathbb{C}_{an}$ be the expansion of the structure $(\mathbb{C}; +,-,×,0,1)$ by adding the restricted complex analytic functions. This is the complex analog of the familiar $\mathbb{R}_{an}$ in O-minimality. What do we know about the model theory of $\mathbb{C}_{an}$? Model-completeness? Quantifier-elimination? etc. PS. It seems Rückert's Nullstellensatz gives us model-completeness (This came to my mind just now) Is this true?

$\endgroup$
9
$\begingroup$

The structure $\mathbb C_{an}$ is bi-interpretable with $\mathbb R_{an}$. To see this, take for example the restriction of the complex exponential function to the unit square S with corners 0,1,i,1+i. Then from this restriction you can define S as the set of points where the restricted function takes a non-zero value. Then the set of complex numbers $x$ satisfying $\forall y[y \in S \to xy \in S]$ is the unit interval [0,1]. Then taking $\pm$ and $1/x$ you can define $\mathbb R$.

So while many people do study restricted holomorphic functions, they do so usually in the context of o-minimality.

$\endgroup$
  • 2
    $\begingroup$ Welcome to [being active on] MathOverflow! $\endgroup$ – Asaf Karagila Feb 23 '18 at 14:55
  • $\begingroup$ Thanks for the useful answer. Do the way by which we interprete $\mathbb{R}_{an}$ in $\mathbb{C}_{an}$ (as you mentioned) and also the way by which we interprete $\mathbb{C}_{an}$ in $\mathbb{R}_{an}$ (I assume this is done by regarding holomorphicity as differentiability), allow us to transfer the model-completeness from one to the other? As I see the formula defining the unit interval has the universal quantifier and the epsilon-delta definition of differentiability is naturally a $\forall_{2}$-formula. $\endgroup$ – shahram Feb 23 '18 at 21:01
  • $\begingroup$ This answer relies on a rather accidental property that you chose to interpret "restricted analytic function" as "restricted to rectangles". It's also easily seen to work for e.g. disks, but what if we take just any odd shape? (Of course, if they shape is too odd, it will be no longer definable in $\mathbb R_{an}$, but I'm only concerned about the other direction.) More precisely: let $D$ be a bounded set with nonempty interior, and define $\mathbb C_{an,D}$ as the expansion of the complex field with restrictions to $D$ of all functions that are analytic in a neighbourhood of $\overline D$... $\endgroup$ – Emil Jeřábek Feb 24 '18 at 11:27
  • $\begingroup$ ... Does $\mathbb C_{an,D}$ interpret $\mathbb R_{an}$ for every $D$? (One can check that without loss of generality, we may assume $D$ to be compact, regular closed (i.e., the closure of its own interior), and simply connected.) $\endgroup$ – Emil Jeřábek Feb 24 '18 at 11:30
  • $\begingroup$ It does work if at least part of the boundary of $D$ is an analytic curve. $\endgroup$ – Emil Jeřábek Feb 24 '18 at 12:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.