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Use this tag when discussing the relative logical strength of axiom sets or foundations of theorem provers

Consistency strength is a measure of the logical power of a system, measuring “how many” statements it can prove. In our context, it refers to the strength of the foundations of a proof assistant or to that of the various theories it might incorporate as modules or whatnot.

A bit more precisely, we say that $T$ has strictly more consistency strength than $T'$ if $T$ proves the existence of a model of $T'$.