History [of sequential substitution systems]
Sequential substitution systems are closely related to the multiway systems discussed on page 938, and are often considered examples of production systems or string rewriting systems. In the form I discuss here, they seem to have arisen first under the name "normal algorithms" in the work of Andrei Markov in the late 1940s on computability and the idealization of mathematical processes. Starting in the 1960s text editors like TECO and ed used sequential substitution system rules, as have string-processing languages such as SNOBOL and perl. Mathematica uses an analog of sequential substitution system rules to transform general symbolic expressions. The fact that new rules can be added to a sequential substitution system incrementally without changing its basic structure has made such systems popular in studies of adaptive programming.