The links to "further information" should probably not be as in an academic paper and dump you onto the bibliography page, where they are not active links.
Let's just go directly to:
- Thom Frühwirth's page on CHR: http://www.constraint-handling-rules.org
- K.U. Leuven: https://dtai.cs.kuleuven.be/CHR/
- Wikipedia: https://en.wikipedia.org/wiki/Constraint_Handling_Rules
- The bibliography page: https://dtai.cs.kuleuven.be/CHR/biblio.shtml