Consider a control system given as a Volterra functional series. Several methods exist in the literature for computing a solution: exponential inputs, association of variables, and formal power series in several noncommutative variables. The authors propose a fourth method based on combinatorics. They provide no details to support their assertion that their method drastically reduces computer computations. Noting that their 15-page paper is too short to explain the theory, they omit proofs. They promise a future paper to explain the theory.