static Exp nlLogic_parseExpression(S s) {
  if (s == null) null;
  L<S> tok = javaTokPlusAllThreeBrackets(s);
  
  // a && b
  PairS p = splitAtTokens_once(tok, ll("&", "", "&"));
  if (p != null)
    ret And(nlLogic_parseExpression(first(p)), nlLogic_parseExpression(second(p)));
    
  // !a
  if (eqGet(tok, 1, "!"))
    ret ExpNot(nlLogic_parseExpression(join(dropFirst(2, tok))));
    
  // function with options - a[bla, blubb](...)
  if (l(tok) == 7 && isIdentifier(tok.get(1))
    && isSquareBracketed(tok.get(3))
    && isRoundBracketed(tok.get(5)))
    ret Func(tok.get(1),
      tok_splitAtComma(deSquareBracket(tok.get(3))),
      nlLogic_parseExpression(deRoundBracket(tok.get(5))));
    
  // function - a(...)
  if (l(tok) == 5 && isIdentifier(tok.get(1)) && isRoundBracketed(tok.get(3))) {
    S name = tok.get(1), arg = deRoundBracket(tok.get(3));
    bool parseInnerPart = false;
    ret Func(name, parseInnerPart ? nlLogic_parseExpression(arg)
      : Sentence2(unquoteIfNormalQuoted(arg)));
  }
    
  // a = b
  LS l = splitAtTokens(tok, ll("="));
  if (l(l) == 2)
    ret Eq(nlLogic_parseExpression(first(l)), nlLogic_parseExpression(second(l)));
    
  // default
  ret Sentence2(l(tok) == 3 && isQuoted(tok.get(1)) ? unquote(second(tok)) : join(tok));
}