# Hopf theorem

> topological degree is the only homotopy invariant of continuous maps to spheres

**Wikidata**: [Q12012849](https://www.wikidata.org/wiki/Q12012849)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Hopf_theorem)  
**Source**: https://4ort.xyz/entity/hopf-theorem


## References

1. Freebase Data Dumps. 2013