Cook, W.R.; Hill, W.L.; Canning, P.S. (January 1990). "Inheritance is not subtyping". Proceedings of the 17th ACM SIGPLAN-SIGACT symposium on Principles of programming languages - POPL '90. San Francisco, California. pp. 125–135. doi:10.1145/96709.96721. ISBN978-0897913430. S2CID8225906.{{cite book}}: CS1 maint: location missing publisher (link)
Cook, W.R.; Hill, W.L.; Canning, P.S. (January 1990). "Inheritance is not subtyping". Proceedings of the 17th ACM SIGPLAN-SIGACT symposium on Principles of programming languages - POPL '90. San Francisco, California. pp. 125–135. doi:10.1145/96709.96721. ISBN978-0897913430. S2CID8225906.{{cite book}}: CS1 maint: location missing publisher (link)