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