code: static boolean isOperationInGroup(int op) {
          switch (op) {
              case PLUS:
              case PLUS_EQUAL:
              case MINUS:
              case MINUS_EQUAL:
              case MULTIPLY:
              case MULTIPLY_EQUAL:
                  return true;
              default:
                  return false;
          }
      }
docs: Returns true for operations that are of the class, that given a common type class for left and right, the
  operation "left op right" will have a result in the same type class In Groovy on numbers that is +,-,* as well as
  their variants with equals.