Karthikeyan Bhargavan Carl A. Gunter Elsa L. Gunter Michael Jackson Davor Obradovic Pamela Zave The Village Telephone System: A Case Study in Formal Software Engineering. 49-66 1998 conf/tphol/1998 TPHOLs db/conf/tphol/tphol98.html#BhargavanGGJOZ98 http://dx.doi.org/10.1007/BFb0055129