
https://papers.ssrn.com/sol3/Delivery.cfm/SSRN_ID3934683_code1082902.pdf?abstractid=3479439&mirid=1

https://bristoluniversitypressdigital.com/downloadpdf/journals/emsoc/4/2/article-p199.xml

https://www.dgb-bestellservice.de/besys_dgb/pdf/DGB15130.pdf