def _ensure_regexp(source, n):  
markers = '<STR_LIT>'<EOL>k = <NUM_LIT:0><EOL>while True:<EOL><INDENT>k += <NUM_LIT:1><EOL>if n - k < <NUM_LIT:0>:<EOL><INDENT>return True<EOL><DEDENT>char = source[n - k]<EOL>if char in markers:<EOL><INDENT>return True<EOL><DEDENT>if char != '<STR_LIT:U+0020>' and char != '<STR_LIT:\n>':<EOL><INDENT>break<EOL><DEDENT><DEDENT>return False<EOL>
returns True if regexp starts at n else returns False
      checks whether it is not a division