import re


def _is_latex(s):
    """

    Decide if a string is a LaTeX expression.

    Args:
        s (str): The string to test.

    Returns:
        bool: True if it seems a LaTeX expression, False otherwise.

    """
    if not s:  # Empty string is not LaTeX
        return False
    return re.match("^.(_.)?$", s) or "\\" in s