“…Upper bound lifespan estimates of solutions to problem () with power nonlinearities , and derivative nonlinearities , are verified in Theorems 1.1 and 1.2. We simplify the proofs of Theorems 1.1 and 1.2 compared with the proofs of the Cauchy problems for single MGT equation in Chen and Palmieri, 4,5 which has been investigated by making use of iteration approach. Namely, it is a special case in problem () with power nonlinearities , and derivative nonlinearities , , when p = q .…”