  For a bivariate $P(x,y) \in \mathbb{R}[x,y]\setminus (\mathbb{R}[x] \cup
\mathbb{R}[y])$, our first result shows that for all finite $A \subseteq
\mathbb{R}$, $|P(A,A)|\geq \alpha|A|^{5/4}$ with $\alpha =\alpha(\mathrm{deg}
P) \in \mathbb{R}^{>0}$ unless $$ P(x,y)=f(\gamma u(x)+\delta u(y)) \text{ or }
P(x,y)=f(u^m(x)u^n(y)) $$ for some univariate $f, u \in \mathbb{R}[t]\setminus
\mathbb{R}$, constants $\gamma, \delta \in \mathbb{R}^{\neq 0}$, and $m, n\in
\mathbb{N}^{\geq 1}$. This resolves the symmetric nonexpanders classification
problem proposed by de Zeeuw. Our second and third results are sum-product type
theorems for two polynomials, generalizing the classical result by Erdos and
Szemer\'edi as well as a theorem by Shen. We also obtained similar results for
$\mathbb{C}$, and from this deduce results for fields of characteristic $0$ and
fields of large prime characteristic. The proofs of our results use tools from
semialgebraic/o-minimal geometry.
