def extract_header(tgt_file):
    """
    Collects lines that don't have a timestep and returns them.

    :param tgt_file: The file to process.
    :return: The headers for the given file.
    """
    with open(tgt_file) as tf:
        h_lines = []
        for t_line in tf:
            s_line = t_line.strip().split()
            if len(s_line) < 2:
                h_lines.append(t_line)
                continue
            try:
                int(s_line[0])
                break
            except ValueError:
                h_lines.append(t_line)
        return h_lines
