static S ai_ruleToJava(S ruleName) {
  S ruleText = unquote(firstPossibleRule(ai_texts("$X", "is", ruleName)));
  if (ruleText == null) fail("Rule not found: " + ruleName);
  S op = joinWithSpace(ai_getOperator(ruleText));
  if (neq(op, "if input * then say *")) fail("Unknown rule op: " + op);
  L<S> l = ai_getOperands(ruleText);
  ret "static S rule_" + wordsToCamelCase(lower(ruleName)) + "() {\n" +
    "  ai_checkInput_match3(" + quote(deRoundBracket(first(l))) + ");\n" +
    "  ret " + quote(deRoundBracket(second(l))) + ";\n" +
    "}";
}