Strength (mathematical Logic)

The relative strength of two systems of formal logic can be defined via model theory. Specifically, a logic $\alpha$ is said to be as strong as a logic $\beta$ if every elementary class in $\beta$ is an elementary class in $\alpha$. 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

Model theory
Mathematical logic
Concepts in logic

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