This example demonstrates a string containment check: given a list of strings, it identifies which elements are substrings of other elements in the list. The code first joins all strings using a separator and then uses recursive string searching to count occurrences. It leverages Python’s built-in `str.find` method within a custom recursive function, `_appear_at_least_n_times`, to efficiently stop searching after finding the required number of matches. The final output is a filtered list containing only those strings that appear at least twice in the combined text, as shown by the example returning `['产科']` for the input `['妇产科', '产科', '儿科']`.