Abstract

The paper presents and discusses an example, namely a version of heterogeneous frrst-order logic and uses the classical theorem of Herbrand-Schmidt-Wang about the reduction of heterogeneous first-order logic to homogeneous first-order logic, in order to obtain two transformations between heterogeneous and homogeneous frrst-order logic which are different from the institution morphisms defined by Goguen and Burstall. Moreover, by considering a type of 2-cell among institution morphisms it is obtained a 2-category and also a 2-functor from this to another 2-category.