“…Algebraic structures based on a central operation of iteration, or feedback -inspired by flowcharts and program schemata -have appeared rather early in computer science, see, e.g., [29,4,89,90,63] and [12], that offers for a thorough exposition of so-called 'iteration theory' and more references. The advent of traced monoidal categories [50], i.e., monoidal categories equipped with a feedback operation completely analogous to the one considered in CM has recently revived interest in using such abstract structures in semantics of computation, as e.g., in [1, 53, 40, 41].…”