Sequence generators, graphs, and formal languages

A sequence generator is a finite graph, more general than, but akin to, the usual state diagram associated with a finite automaton. The nodes of a sequence generator represent complete states, and each node is labeled with an input and an output state. An element of the behavior of a sequence generator is obtained by taking the input and output states along an infinite path of the graph.Sequence generators may be associated with formulas of the monadic predicate calculus, in which the individual variables range over the times 0, 1, 2, 3, ···, and the predicate variables represent complete states, input states, and output states. An unrestricted singulary recursion is a formula in which the complete state at time τ + 1 is expressed as a truth-function of the complete state at time τ and the input states from times τ + 1 to τ + h. Necessary and sufficient conditions are given for a formula derived from a sequence generator being equivalent to an unrestricted singulary recursion