To cite package ‘exdex’ in publications use:

  Northrop PJ, Christodoulides C (2023). _exdex: Estimation of the
  Extremal Index_. R package version 1.2.3, ,
  <https://github.com/paulnorthrop/exdex>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {exdex: Estimation of the Extremal Index},
    author = {Paul J. Northrop and Constantinos Christodoulides},
    year = {2023},
    note = {R package version 1.2.3, 
},
    url = {https://github.com/paulnorthrop/exdex},
  }