The Size-Change Termination Principle for Constructor Based Languages

foetus —— 面向简单函数式程序的终止性检查器

foetus -- Termination Checker for Simple Functional Programs

本研究提出带终止性检查器的函数式语言foetus，通过提取函数调用、补全调用图并寻找参数良基结构序，来证明简单函数式程序的终止性。

On the relation between size-based termination and semantic labelling

We investigate the relationship between two independently developed termination techniques. On the one hand, sized-types based termination (SBT) uses types annotated with size expressions and Girard's reducibility candidates, and applies on systems using constructor matching only. On the other hand, semantic labelling transforms a rewrite system by annotating each function symbol with the semantics of its arguments, and applies to any rewrite system. First, we introduce a simplified version of SBT for the simply-typed lambda-calculus. Then, we give new proofs of the correctness of SBT using se…

Generating induction principles and subterm relations for inductive types using MetaCoq

We implement three Coq plugins regarding inductive types in MetaCoq. The first plugin is a simple syntax transformation generating alternative constructors for inductive types by abstracting over concrete indices in the types of the constructors. The second plugin re-implements Coq's $\texttt{Scheme Induction}$ command in MetaCoq, and extends it to nested inductive types, e.g. types like rose trees which use $\texttt{list}$ in their definition, similar to the Elpi-plugin by Tassi. The third plugin implements the $\texttt{Derive Subterm}$ command provided by the Equations package in MetaCoq.

Termination of $λ$$Π$ modulo rewriting using the size-change principle (work in progress)

The Size-Change Termination principle was first introduced to study the termination of first-order functional programs. In this work, we show that it can also be used to study the termination of higher-order rewriting in a system of dependent types extending LF.

Dependent choice as a termination principle

We introduce a new formulation of the axiom of dependent choice that can be viewed as an abstract termination principle, which generalises the recursive path orderings used to establish termination of rewrite systems. We consider several variants of our termination principle, and relate them to general termination theorems in the literature.

Practical Subtyping for System F with Sized (Co-)Induction

We present a rich type system with subtyping for an extension of System F. Our type constructors include sum and product types, universal and existential quantifiers, inductive and coinductive types. The latter two size annotations allowing the preservation of size invariants. For example it is possible to derive the termination of the quicksort by showing that partitioning a list does not increase its size. The system deals with complex programs involving mixed induction and coinduction, or even mixed (co-)induction and polymorphism (as for Scott-encoded datatypes). One of the key ideas is to…