We are happy to announce that the following article has been accepted to the 42nd International Conference on Formal Techniques for Distributed Objects, Components, and Systems (FORTE'22), one of the three conference of the 17th International Federated Conference on Distributed Computing Techniques (DisCoTec'22) to be held on June 13-17 in Lucca, Italy. (Philipp will go there to present the paper.) ====================================================================== LTL under reductions with weaker conditions than stutter invariance Emmanuel Paviot-Adet (1)(2), Denis Poitrenaud (1)(2), Etienne Renault (3), Yann Thierry-Mieg (1) (1) SorbonneUniversité,CNRS,LIP6,F-75005Paris,France (2) Université de Paris,F-75006Paris,France (3) LRDE, EPITA, France Verification of properties expressed as 𝜔-regular languages such as LTL can benefit hugely from stutter insensitivity, using a diverse set of reduction strategies. However properties that are not stutter invariant, for instance due to the use of the neXt operator of LTL or to some form of counting in the logic, are not covered by these techniques in general. We propose in this paper to study a weaker property than stutter insensitivity. In a stutter insensitive language both adding and removing stutter to a word does not change its acceptance, any stuttering can be abstracted away; by decomposing this equivalence relation into two implications we obtain weaker conditions. We define a shortening insensitive language where any word that stutters less than a word in the language must also belong to the language. A lengthening insensitive language has the dual property. A semi-decision procedure is then introduced to reliably prove shortening insensitive properties or deny lengthening insensitive properties while working with a reduction of a system. A reduction has the property that it can only shorten runs. Lipton’s transaction reductions or Petri net agglomerations are examples of eligible structural reduction strategies. An implementation and experimental evidence is provided showing most non- random properties sensitive to stutter are actually shortening or lengthening in- sensitive. Performance of experiments on a large (random) benchmark from the model-checking competition indicate that despite being a semi-decision proce- dure, the approach can still improve state of the art verification tools. https://www.lrde.epita.fr/wiki/Publications/paviot.22.forte <https://www.lrde.epita.fr/wiki/Publications/paviot.22.forte>