def _to_lower_alpha_only(s):
s = re.sub(r'<STR_LIT:\n>', '<STR_LIT:U+0020>',  s.lower())<EOL>return re.sub(r'<STR_LIT>', '<STR_LIT>', s)<EOL>
Return a lowercased string with non alphabetic chars removed.

    White spaces are not to be removed.