code: protected static boolean isOperatorLR( Symbol s ) {
          if( s == null )
              return false;
  
          switch( s ) {
              case ELEMENT_DIVIDE:
              case ELEMENT_TIMES:
              case ELEMENT_POWER:
              case RDIVIDE:
              case LDIVIDE:
              case TIMES:
              case POWER:
              case PLUS:
              case MINUS:
              case ASSIGN:
                  return true;
          }
          return false;
      }
docs: Operators which affect the variables to its left and right