Abstract Finding semantic bugs in code is difficult and requires precious expert time. Lacking comprehensive formal specifications, deductive verification is not an option. We propose an incremental specification procedure: With the help of automatic verification tools, a domain expert is guided through program runs and source code locations. The expert validates a run at certain locations and creates lightweight annotations. Formal methods training is not required. We demonstrate by example that this approach is capable to quickly detect different kinds of semantic bugs. We position our approach in the middle ground between fully-fledged deductive verification and bug finding without semantic guidance.

Abstract Novel three-valued non-deterministic level semantics for modal logics $\textbf {T}$ and $\textbf {S4}$ are presented. A criterion for partial level valuations is given, making it possible to create truth tables. Additionally, semantics and truth tables for $\textbf {0}$ (defined as $\textbf {PC}$ plus rule of necessitation) and $\textbf {0T}$ with only two values are based on Ivlev’s work. We need Kearns’ notion of level valuations: a generalization of Dugundji’s theorem shows that there is no non-deterministic semantics for modal logics up to $\textbf {S5}$, containing the rule of necessitation.