cross_fit_helper        Helper function to for cross-fitting
custom_helper           Custom generator
double_ML               Post double selection.
fit_cross               Cross-fitting helper
glmnet_helper           Helper function(glmnet).
input_checker           Helper function for input checking
nn_helper               Helper function for neural networks fitted by
                        neuralnet
ols_helper              Helper function(least squares).
plot_ML                 Plot the fitted Debiased ML treatment effects.
rf_helper               Helper function(randomforest).
