31. Robert Solovay proved that the modal logic GL is complete with respect to Peano Arithmetic. 32. Tableaux calculi for modal logic take into account that formulae may refer to different worlds. 33. Modal logic is most commonly interpreted in terms of possible world semantics or Kripke structures.34. There is also an intuitionistic version of modal logic S4 called Constructive Modal Logic CS4. 35. This is necessarily true of all classical modal logics . 36. There is also an intuitionistic version of modal logic S4 called Constructive Modal Logic CS4. 37. Modal logics are generally characterized by invariances under bisimulation.38. Formal ethics has four axioms in addition to the axioms of predicate and modal logic . 39. Modal logics is another approach which also applies .)40. Modal logic also offers a variety of inferences that cannot be captured in propositional calculus.
