Jancar's formal system for deciding bisimulation of first-order grammars   and its non-soundness
  We construct an example of proof within the main formal system from arXiv:1010.4760v3, which is intended to capture the bisimulation equivalence for non-deterministic first-order grammars, and show that its conclusion is semantically false. We then locate and analyze the flawed argument in the soundness (meta)-proof of the above reference. 
G\'eraud S\'enizergues (Bordeaux, France)
cs.FL cs.LO