def is_natural_language(line):
    """Determine if a line is likely to be actual natural language text, as
    opposed to, e.g., LaTeX formulas or tables.  Pretty crude heuristic, but as
    long as it filters out most of the bad stuff it's okay, I guess."""
    line = line.strip()
    if len(line) < 5:
        return False
    if "\\" in line or line[0] == "$" or line[-1] == "$":
        # probably contains a LaTeX formula; skip
        return False
    if line.count(" ") < 2:
        # maybe a headline, or a fragment
        return False
    if "   " in line or not line.replace("-", "").strip():
        # table?
        return False
    return True