Eighteenth Annual IEEE Symposium on

Logic in Computer Science (LICS 2003)

Paper: Structural Subtyping of Non-Recursive Types is Decidable (at LICS 2003)

Authors: Viktor Kuncak Martin Rinard


We show that the first-order theory of structural subtyping of non-recursive types is decidable, as a consequence of a more general result on the decidability of term powers of decidable theories. Let \Sigma be a language consisting of function symbols and let C (with a finite or infinite domain C) be an L-structure where L is a language consisting of relation symbols. We introduce the notion of \Sigma-term-power of the structure C, denoted P(C). The domain of P(C) is the set of \Sigma-terms over the set C. P(C) has one term algebra operation for each f \in \Sigma, and one relation for each r \in L defined by lifting operations of C to terms over C. We extend quantifier elimination for term algebras and apply the Feferman-Vaught technique for quantifier elimination in products to obtain the following result. Let K be a family of L-structures and K the family of their \Sigma-term-powers. Then the validity of any closed formula F on K can be effectively reduced to the validity of some closed formula q(F) on K. Our result implies the decidability of the first-order theory of structural subtyping of non-recursive types with co-variant constructors, and the construction generalizes to contravariant constructors as well.


    author = 	 {Viktor Kuncak and Martin Rinard},
    title = 	 {Structural Subtyping of Non-Recursive Types is Decidable},
    booktitle =  {Proceedings of the Eighteenth Annual IEEE Symp. on Logic in Computer Science, {LICS} 2003},
    year =	 2003,
    editor =	 {Phokion G. Kolaitis},
    month =	 {June}, 
    pages =      {96--107},
    location =   {Ottawa, Canada}, 
    publisher =	 {IEEE Computer Society Press}