 The logics in those two classes have the following property: the Tarski relation of every full g-model \(\langle \bA, C \rangle\) is \(\{\langle a, b \rangle \in A \times A: C(a) = C(b)\}\). A way of saying it is to say that for these logics the property that defines selfextensionality, namely that the interderivability condition is a congruence, lifts or transfers to every full g-model. The selfextensional logics with this property are called fully selfextensional. This notion was introduced in Font &amp; Jansana 1996 under the name ‘strongly selfextensional’. All the natural selfextensional logics considered up to 1996 are fully selfextensional, in particular the logics discussed in  Section 12,  but Babyonyshev showed (Babyonyshev 2003) an ad hoc example of a selfextensional logic that is not fully selfextensional. A much more natural example discovered later of a selfextensional logic that is not fully selfextensional is the fragment of only the negation and the constant \(\top\) of classical logic. 