Analogies of PAL and COPY

Abstract

The LIFO or pushdown principle and the FIFO or queue principle are compared in the framework of language theory. To this effect, languages which characteristically describe these principles are studied comparing the least cones or semiAFLs containing them. Although the classes of languages so obtained are different and often are incomparable, very interesting analogies are established between LIFO type languages and FIFO type languages. Thus our investigations show both, the common and the contrasting properties of LIFO and FIFO structures.