Consideration is given to the problem of maze routing: compilation of a route that delivers us from an arbitrary point to a given one. A class of mazes subject to routing (namely, a class of mazes for which the problem of routing can be solved) is described.

Extension of an addition-semigroup of natural numbers to a field is shown to be a special case of the extension, of a set of terms to a set of infinite terms. Here, rational terms correspond to the rational numbers.

The paper presents an informal description of weak monadic theories of the second order with multiple successor relations and the notion of rational term. The potentials of the language of these theories in describing complex dale structures are illustrated by examples. The existing means of specification are shown to be special cases of the weak monadic theories.