def backward(self, summation: Variable, backward_engine: EngineLM):
        """
        Performs the backward pass of the sum operation.
        This is simply an idempotent operation, where we pass the feedback to the predecessors variables.

        :param summation: The variable representing the sum.
        :type summation: Variable
        :param backward_engine: The backward engine used for backpropagation.
        :type backward_engine: EngineLM
        """
        children_variables = summation.predecessors
        summation_gradients = summation.get_gradient_text()
        for variable in children_variables: 
            if summation_gradients == "":
                variable_gradient_value = ""
            else:
                variable_gradient_value = f"Here is the combined feedback we got for this specific {variable.get_role_description()} and other variables: {summation_gradients}."
                
            logger.info(f"Idempotent backward", extra={"v_gradient_value": variable_gradient_value, 
                                                    "summation_role": summation.get_role_description()})

            var_gradients = Variable(value=variable_gradient_value, 
                                    role_description=f"feedback to {variable.get_role_description()}")
            variable.gradients.add(var_gradients)
            
            if summation._reduce_meta != []:
                var_gradients._reduce_meta.extend(summation._reduce_meta)
                variable._reduce_meta.extend(summation._reduce_meta)

            variable.gradients.add(Variable(value=variable_gradient_value, 
                                            role_description=f"feedback to {variable.get_role_description()}"))

        Performs the backward pass of the sum operation.
        This is simply an idempotent operation, where we pass the feedback to the predecessors variables.

        :param summation: The variable representing the sum.
        :type summation: Variable
        :param backward_engine: The backward engine used for backpropagation.
        :type backward_engine: EngineLM
        
textgrad/autograd/algebra.py