Extending H1H1-clauses with disequalities

The class H1H1 has proven particularly useful for the analysis of term-manipulating programs such as cryptographic protocols. Here, we show that clauses from that class can be extended with disequalities between arbitrary terms while retaining decidability of satisfiability. The proof is based on a normalization procedure together with a procedure to decide whether a finite automaton with disequalities accepts less than k elements, and a subtle combinatorial argument to prove that only finitely many disequalities need to be considered.

► We extend H1H1-clauses with disequalities between arbitrary terms.
► We show that satisfiability of H1H1-clauses with disequalities still is decidable.
► For that, we use a normalization procedure that simplifies the clauses.