METATHEORY
Formal systems studied as objects, rather than reasoning conducted within any one of them. Its entries are the theories, techniques, and theorems by which logics are given semantics, their proofs analyzed, their models constructed, and the limits of computation and provability established.
The division is organized by the object of metatheoretic study. Model-Theory entries treat satisfaction, definability, and the construction and classification of models. Proof-Systems entries treat calculi, normalization, and the structure of derivations. Categorical entries treat logics through category theory and their categorical semantics. Computability entries treat the theory of the computable and the degrees of unsolvability.