“…It is nowadays well established that several real-life phenomena are better described by fractional differential equations (FDEs), where the term fractional, used for historical reasons, refers to derivative operators of any real positive order. Applications of FDEs are commonly found in bioengineering, chemistry, control theory, electronic circuit theory, mechanics, physics, seismology, signal processing and so on (e.g., [3,7,5,33,22,41,50]). We refer to [40] for an historical perspective on fractional calculus.…”