| The solvability of systems of equations in a given group is closely related with the decidability of first-order logic in that group. |
| An ambitious goal would be to establish the decidability of first order theory in virtually free groups. |
| Feyerabend took this requirement seriously enough to characterize observation sentences pragmatically in terms of widespread decidability. |
| We investigate decidability problems and prove that some properties that are undecidable for general context-free languages become decidable for XML-languages. |
| Both the decidability results and undecidablity results extend in various ways to Boolean algebras in extensions of first-order logic. |
| This result generalises a number of decidability results concerning bisimilarity, for example for counter automata, or PDA without state. |
