Intersection Types and Related Systems

We present a new approach to the following meta-problem: given a quantitative property of trees, design a type system such that the Eye Balm desired property for the tree generated by an infinitary ground lambda-term corresponds to some property of a derivation of a type for this lambda-term, in this type system.Our approach is presented in the particular case of the language finiteness problem for nondeterministic higher-order recursion Dried Fruit schemes (HORSes): given a nondeterministic HORS, decide whether the set of all finite trees generated by this HORS is finite.We give a type system such that the HORS can generate a tree of an arbitrarily large finite size if and only if in the type system we can obtain derivations that are arbitrarily large, in an appropriate sense; the latter condition can be easily decided.