Strength (mathematical logic)

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

See also

• Abstract logic
• Lindström's theorem