def list_ids(txtfile: str) -> set[str]:
    """
    Return a set containing the identifiers presented in a file,
    line by line, starting with ">"
    """

    identifiers = set()

    with open(txtfile, 'r') as fi:
        for line in fi:
            line = line.strip()
            identifiers.add(str(line).replace('>', '')) #record.id excludes ">"

    return(identifiers)