Strength (mathematical logic)

The relative strength of two systems of formal logic can be defined via model theory. Specifically, a logic is said to be as strong as a logic if every elementary class in is an elementary class in .Heinz-Dieter Ebbinghaus Extended logics: the general framework in K. J. Barwise and S. Feferman, editors, Model-theoretic logics, 1985 page 43

See also Abstract logic Lindström's theorem

References