Issue on page /22-Debiased-Orthogonal-Machine-Learning.html

[0scarrrrr]

I am not sure that the example in What is Non-Parametric About? is correct

As you stay Sales_i = 20+10*Discounts^0.5 + ei

However this is linear in the parameters and not linear in the covariates

as delta_sales_i / delta_discounts_i = 5*Discounts^(-0.5) - 5 being the parameter and Discounts being the covariate, therefore any estimator of the such Y = tau(Xi)*T + ei should be able to learn that T = 5 and tau = Xi^-0.5

Am I missing something?