Abstract

This paper proves the decidability of subtyping for F when the bounds on polymorphic types do not contain Top (i.e., in all types of the form 8ff!:ø 1 :ø 2 , ø 1 does not contain Top). This general restriction is subsequently relaxed to allow unbounded quantification. 1 Introduction F [CW85,CG] is a typed -calculus with subtyping and bounded second-order polymorphism. The importance of F in programming language design is that it provides a simple context for studying the typing problems that arise when subtyping and bounded quantification are added to polymorphic languages such as ML. Curien and Ghelli [CG] recently developed a subtyping algorithm for F and proved its partial correctness. Subsequently, Ghelli [Ghe90] presented a termination proof for this algorithm. A mistake was discovered in this termination proof, following which Pierce [Pie92] presented a proof showing that the subtyping problem for general F types is undecidable. This paper shows how one can make the subtyping p...

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