def get_min_col_num(mention):
span = _to_span(mention)<EOL>if span.sentence.is_tabular():<EOL><INDENT>return span.sentence.cell.col_start<EOL><DEDENT>else:<EOL><INDENT>return None<EOL><DEDENT>
Return the lowest column number that a Mention occupies.

    :param mention: The Mention to evaluate. If a candidate is given, default
        to its first Mention.
    :rtype: integer or None