APA (7th ed.) Citation
(1991). Tunnelling '91: The 6th international symposium./ London, England, 14.-18.4.1991. Elsevier.
Chicago Style (17th ed.) Citation
Tunnelling '91: The 6th International Symposium./ London, England, 14.-18.4.1991. London: Elsevier, 1991.
MLA (9th ed.) Citation
Tunnelling '91: The 6th International Symposium./ London, England, 14.-18.4.1991. Elsevier, 1991.
Warning: These citations may not always be 100% accurate.