Peritropè

A peritropè describes a state of affairs in which an assertion is made, the refutation of which, paradoxically, supports the assertion itself.

An example can be found in the assertion “At least one assertion is true”. Namely, on the assumption that the opposite - “all assertions are wrong” - is correct, a true assertion (that is to say that all assertions are false) is made again. Along with all the other false claims, at least one claim is true.