“…In recent times, researchers have given the existence, uniqueness, and Ulam stability of solutions for differential equations and systems of arbitrary order; see [
17–36]. In recent years, many scientific researchers have considered differential equations and systems containing sequential fractional derivatives of different types; for instance, see [
37–44]. In [
6], for differential equations the existence and uniqueness of solutions with Caputo fractional derivatives of different orders have been given as
…”