that’s it. the body and tail advance together through each character, and when the body finally becomes nullable the lookahead dissolves and only the tail remains. the actual implementation is slightly more involved, but the idea is all here.
Летящий из России во Вьетнам самолет подал сигнал бедствия20:53，更多细节参见91吃瓜
第二，国内重要领域重点单位就业率超过86%，连续16年保持在80%以上。，更多细节参见谷歌
fn find_positive(numbers: [int]) - ?int {