<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def unquote_pre_filter(pre_filter, _regex=re.compile(r'[\\]+')):
 """ Unquote a pre-filter condition. """

    if pre_filter.startswith('"') and pre_filter.endswith('"'):
        # Unquote outer level
        pre_filter = pre_filter[1:-1]
        pre_filter = _regex.sub(lambda x: x.group(0)[:len(x.group(0)) // 2], pre_filter)

    return pre_filter