“…We assume that (u, v) = (u(x, t), v(x, t)), is a local solution to (2). In order to prove the lifespan estimate, we replace the initial data (0, u 1 , u 2 ), (0, v 1 , v 2 ) by (0, εf 1 , εf 2 ), (0, εg 1 , εg 2 ) with a small constant ε > 0, where (11). Repeating the steps in the above proofs, we arrive at the following estimate:…”