“…Recently, the results of the first experiments on its discovery in the reactions [30], (e) J/ψ → φf 0 (980)π 0 → φ 3π [31], (f) J/ψ → φf 1 (1285) → φf 0 (980)π 0 → φ 3π [31] have been obtained with the help of detectors VES in Protvino [27,28] and BESIII in Beijing [29][30][31]. The theoretical considerations concerning the BESIII data [30] * achasov@math.nsc.ru † kozhev@math.nsc.ru ‡ shestako@math.nsc.ru on the reaction (d), that is, on the decay η(1405) → f 0 (980)π 0 → 3π, were presented in [32][33][34][35]. Interest in the a 0 0 (980) − f 0 (980) mixing is primarily due to the fact that the amplitude of the isospin breaking transition a 0 0 (980) → (K + K − + K 0K 0 ) → f 0 (980), caused by the mass difference of the K + K − and K 0K 0 intermediate states, in the region between KK thresholds turns out to be of the order of (m K 0 − m K + )/m K 0 [1] [i.e.…”