The HM(X) framework is a constraint-based type framework with built-in let-polymorphism. This paper establishes purely syntactic type soundness for the framework, treating an extended version of the language containing state and recursive binding. These results demonstrate that any instance of HM(X), comprising a specialized constraint system and possibly additional functional constants and their types, enjoys syntactic type soundness. © 2003 Published by Elsevier Science B.V.
Skalka, C., & Pottier, F. (2003). Syntactic type soundness for HM(X). In Electronic Notes in Theoretical Computer Science (Vol. 75, pp. 61–74). Elsevier B.V. https://doi.org/10.1016/S1571-0661(04)80779-5