I am working my way for the first time through predicting a continuous dependent variable in a problem where all independent variables are categorical using python statsmodels. I would like to add to this model 'y ~ + C(x1) + C(x2) + C(x3)' all possible quadratic terms. What is the right notation for that?
EDIT: one of my categorical variables is age, which I binned in four different bins. All other are transformed into dummy. So the idea was to square age.