Giuseppe Castagna. Covariance and Contravariance: Conflict without a Cause. ACM Transactions on Programming Languages and Systems, 17(3):431-447, 1995. [doi]
@article{Castagna95,
title = {Covariance and Contravariance: Conflict without a Cause},
author = {Giuseppe Castagna},
year = {1995},
doi = {10.1145/203095.203096},
url = {http://doi.acm.org/10.1145/203095.203096},
researchr = {https://researchr.org/publication/Castagna95},
cites = {0},
citedby = {0},
journal = {ACM Transactions on Programming Languages and Systems},
volume = {17},
number = {3},
pages = {431-447},
}