public class LogicBinary extends Binary {
  public Object sem (String op) throws SemanticException {
    super.sem();
    if (aT == Integer.class && bT == Integer.class) return T = Integer.class;
    if (aT == Boolean.class && bT == Boolean.class) return T = Boolean.class;
    throw new SemanticException("binary "+ op +" expects boolean or int");
  }
}