“…These results were generalized by Fei, Kim and Wong [58]. The method of Mawhin and Willem was adapted by Tang [121], Zhang and Zhou [156,157], Meng and Tang [93] and Tang and Wu [130] to find conditions for existence of solutions to a system with a subquadratic growth condition, including subadditive and subconvex potentials. The method was adapted by Ma and Tang [89], Wu and Zhao [148,149], Jiang and Tang [74], Tang and Ye [132], and Tang and Wu [130] to find conditions for existence of solutions to a system with a quadratically bounded potential.…”