English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Zendy Plus

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Zendy Tools

Zendy Open

A function $f:\RR^n \to \RR$ is called \emph{vertically rigid} if $graph(cf)$is isometric to $graph (f)$ for all $c \neq 0$. We settled Jankovi\'c'sconjecture in a separate paper by showing that a continuous function $f:\RR \to\RR$ is vertically rigid if and only if it is of the form $a+bx$ or $a+be^{kx}$($a,b,k \in \RR$). Now we prove that a continuous function $f:\RR^2 \to \RR$ isvertically rigid if and only if after a suitable rotation around the z-axis$f(x,y)$ is of the form $a + bx + dy$, $a + s(y)e^{kx}$ or $a + be^{kx} + dy$($a,b,d,k \in \RR$, $k \neq 0$, $s : \RR \to \RR$ continuous). The problemremains open in higher dimensions.

The structure of continuous rigid functions of two variables