Altidor, John; Shan, Huang Shan; Smaragdakis, Yannis (2011). "Taming the wildcards: combining definition- and use-site variance". Proceedings of the 32nd ACM SIGPLAN conference on Programming language design and implementation (PLDI'11). ACM. pp. 602–613. CiteSeerX10.1.1.225.8265. doi:10.1145/1993316.1993569. ISBN9781450306638.
Igarashi, Atsushi; Viroli, Mirko (2002). "On Variance-Based Subtyping for Parametric Types". Proceedings of the 16th European Conference on Object-Oriented Programming (ECOOP '02). Lecture Notes in Computer Science. Vol. 2374. pp. 441–469. CiteSeerX10.1.1.66.450. doi:10.1007/3-540-47993-7_19. ISBN3-540-47993-7.
Thorup, Kresten Krab; Torgersen, Mads (1999). "Unifying Genericity: Combining the Benefits of Virtual Types and Parameterized Classes". Object-Oriented Programming (ECOOP '99). Lecture Notes in Computer Science. Vol. 1628. Springer. pp. 186–204. CiteSeerX10.1.1.91.9795. doi:10.1007/3-540-48743-3_9. ISBN3-540-48743-3.
Franz Weber (1992). "Getting Class Correctness and System Correctness Equivalent - How to Get Covariance Right". TOOLS 8 (8th conference on Technology of Object-Oriented Languages and Systems), Dortmund, 1992. CiteSeerX10.1.1.52.7872.
Altidor, John; Shan, Huang Shan; Smaragdakis, Yannis (2011). "Taming the wildcards: combining definition- and use-site variance". Proceedings of the 32nd ACM SIGPLAN conference on Programming language design and implementation (PLDI'11). ACM. pp. 602–613. CiteSeerX10.1.1.225.8265. doi:10.1145/1993316.1993569. ISBN9781450306638.
Igarashi, Atsushi; Viroli, Mirko (2002). "On Variance-Based Subtyping for Parametric Types". Proceedings of the 16th European Conference on Object-Oriented Programming (ECOOP '02). Lecture Notes in Computer Science. Vol. 2374. pp. 441–469. CiteSeerX10.1.1.66.450. doi:10.1007/3-540-47993-7_19. ISBN3-540-47993-7.
Thorup, Kresten Krab; Torgersen, Mads (1999). "Unifying Genericity: Combining the Benefits of Virtual Types and Parameterized Classes". Object-Oriented Programming (ECOOP '99). Lecture Notes in Computer Science. Vol. 1628. Springer. pp. 186–204. CiteSeerX10.1.1.91.9795. doi:10.1007/3-540-48743-3_9. ISBN3-540-48743-3.