# Hilbert's fourth problem

> one of twenty-three, asking to construct all metric spaces where lines resemble those on a sphere

**Wikidata**: [Q4515035](https://www.wikidata.org/wiki/Q4515035)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Hilbert's_fourth_problem)  
**Source**: https://4ort.xyz/entity/hilbert-s-fourth-problem