Pag 46 says: He begins to do a rethink about what is a function. Function is a rule? If it is a rule then: f(x) = x² and f(x) = x² +3x + 3 -3(x+1) are different. But that was not what we wanted. But he rewrites, this way: f(x) = x² and f(x) = x² +3x +3 -c(x+1) Apparently this was a small mistake. I would like to hear the opinion of colleagues. Thank you.