Interpretability logic

Interpretability logics comprise a family of modal logics that extend provability logic to describe interpretability or various related metamathematical properties and relations such as weak interpretability, Π1-conservativity, cointerpretability, tolerance, cotolerance, and arithmetic complexities. Main contributors to the field are Alessandro Berarducci, Petr Hájek, Konstantin Ignatiev, Giorgi Japaridze, Franco Montagna, Vladimir Shavrukov, Rineke Verbrugge, Albert Visser, and Domenico Zambella. The language of ILM extends that of classical propositional logic by adding the unary modal operator and the binary modal operator (as always, is defined as ). The arithmetical interpretation of is “ is provable in Peano arithmetic (PA)”, and is understood as “ is interpretable in ”. Axiom schemata:

1. All classical tautologies

Rules of inference:

1. “From and conclude ”
2. “From conclude ”. The completeness of ILM with respect to its arithmetical interpretation was independently proven by Alessandro Berarducci and Vladimir Shavrukov. The language of TOL extends that of classical propositional logic by adding the modal operator which is allowed to take any nonempty sequence of arguments. The arithmetical interpretation of is “ is a tolerant sequence of theories”. Axioms (with standing for any formulas, for any sequences of formulas, and identified with ⊤):
3. All classical tautologies

Rules of inference:

1. “From and conclude ”
2. “From conclude ”. The completeness of TOL with respect to its arithmetical interpretation was proven by Giorgi Japaridze.