Recent research has shown how boilerplate code, or repetitive code for traversing datatypes, can be eliminated using generic programming techniques already available within some implementations of Haskell. One particularly intractable kind of boilerplate is nameplate, or code having to do with names, name-binding, and fresh name generation. One reason for the difficulty is that operations on data structures involving names, as usually implemented, are not regular instances of standard map, fold , or zip operations. However, in nominal abstract syntax, an alternative treatment of names and binding based on swapping, operations such as #-equivalence, capture-avoiding substitution, and free variable set functions are much better-behaved.

Static type systems in programming languages allow many errors to be detected at compile time that wouldn't be detected until runtime otherwise. Dependent types are more expressive than the type systems in most programming languages, so languages that have them should allow programmers to detect more errors earlier. In this paper, using the Twelf system, we show that dependent types in the logic programming setting can be used to ensure partial correctness of programs which implement theorem provers, and thus avoid runtime errors in proof search and proof construction. We present two examples: a tactic-style interactive theorem prover and a union-find decision procedure.

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The most general unifier (MGU) of a pair of terms can be specified by four axioms. In this paper we generalize the standard presentation of the axioms to specify the MGU of a list of equational constraints and we formally verify that the unification algorithm satisfies the axioms. Our constraints are equalities between terms in a language of simple types. We model substitutions as finite maps from the Coq library Coq.FSets.FMapInterface. Since the unification algorithm is general recursive we show termination using a lexicographic ordering on lists of constraints. Coq’s method of functional induction is the main proof technique used in proving the axioms. 1