in june of the same year , zhao renkai , han duo -lsb- 7281 6995 -rsb- and li lefu -lsb- 2621 2867 4395 -rsb- , under the supervision of peng huanwu -lsb- 1756 2719 2976 -rsb- , repeatedly investigated , calculated , and deliberated the problems before proposing the `` nuclear submarine power device design -lrb- draft -rrb- . ''