public function isAnInExpression(TreeExpression $expr)
    {
        $count = $expr->count();
        if ($count <= 1 || strtolower($expr->getValue()) != 'or' )
            return false;

        $children = $expr->getChildren();
        if (!$children[0] instanceof FieldExpression)
            return false;

        for ($i = 1; $i < $count; $i++) {
            if (!$children[$i] instanceof FieldExpression)
                return false;
            if ($children[$i]->getField() != $children[$i-1]->getField())
                return false;
        }

        return true;
    }